Tackle Zones Pt2 – Screening

Posted by Wulfyn on 16th January 2018

Introduction

In the first article of this series we took a look at how tackle zones help when tagging and marking opposition players. But we also saw how tackle zones denied the other coach space for their team to move into, by making the chance of their players moving into that space very low. In this article we look more at how to do this, how different formations change that chance, and try to highlight the fundamental principles behind this structure. Once again we start at first principles, so apologies to veteran coaches who will already have grasped everything here.

 

Firstly we’ll be using the same markings as before. Blue squares will be used to pick out movement opportunities to highlight weak points. Green will be used for one tackle zone, yellow for two, orange for three, and red for four or more:

 

Let’s first take a look at the pattern of tackle zones for different screens. For a quick summary of their strength we’ll look at the chance of an Ag3 player with a team reroll and no skills to dodge through the screen (not around it). There is a lot more to the strengths and weaknesses than this simple calculation, but again we have to start somewhere so we’ll keep things basic for now.

 

Closed Screens (no gap)

Closed Screen, same rank = 0%

Closed Screen, 1 rank = 44%

 

Tight Screens (1 square gap)

Tight Screen, same rank = 28%

Tight Screen, 1 rank = 61%

Tight Screen, 2 ranks = 89%

 

Loose Screens (2 square gap)

Loose Screen, same rank = 39%

Loose Screen, 1 rank = 61%

Loose Screen, 2 ranks = 89%

Loose Screen, 3 ranks = 100%

 

Results

We didn’t go 3 ranks back for all examples as these are symmetrical to wider screens. We can summarise the results in a table:

 Closed ScreenTight ScreenLoose Screen
Same rank          0%       28%       39%
1 rank back       44%       61%       61%
2 ranks back          –       89%       89%
3 ranks back          –          –     100%

 

So what do we make of this? We see that the chance of getting through improves when the screen is wider and players are offset by ranks. But second we notice that when looking at a tight and loose screen the chances for 1 and 2 ranks are the same across both widths. That means that a loose screen is no worse than a tight screen when the players are 1 or 2 ranks apart. Finally we notice that the weakening of the screen is quite large for each extra rank, meaning that there will be a marked effect on the game (a few percentage points, whilst optimal, doesn’t present a large impact on an entire game, but 30%pts is significant).

This leads us to our first conclusion – screens should always be on the same rank.

 

The Blitz!

The above, whilst a good start, is not realistic of a game situation because screening players can be removed by your blitzing player. Every single formation above improves to a 100% chance of getting through if the blitzing player knocks down the defender. And because the blitzing player usually has a good choice of which screening player they want to knock down, the only realistic solution is to create a second screen behind the first.

If either of the front players are removed we still have a screen from the second rank of players.

 

This approach is therefore, unsurprisingly, a common staple among blood bowl coaches known as the column defence. The double screen means that whilst a blitz is required to improve the chance of a player dodging through, it is at best only as good as the ‘same rank’ statistic of whichever width of screen you have selected. Let’s look at an Undead team trying to break through a column defence on the final turn of a game.

Undead players have a yellow skill ring, other than the ball carrying Ghoul who has a white skill ring.

First the Zombie moves up to tag the front line-rat to place an assist.

Then the Wight blitzes the front rat.

 

The rat is knocked down, and with the loss of its tackle zones we see that we effectively have a same rank wide screen across the back rank of players. Here the Ghoul would dodge down the side line (49% with team reroll, 39% without). Note that this attack is symmetrical – it would not matter which of the front rats the Wight knocks down, nor which channel that Ghoul runs down from it (even with a push). We could have hit the centre rat to the right and then had the ghoul run down the 4th column and it would be the same odds. And whilst a 50/50(ish) of preventing the score isn’t great, it’s not terrible either.

 

Now let’s consider if the screen was set up with one of the columns slightly off rank:

We know from the above analysis that the diagonals are weaker, so we will target the space between the centre column and the left column of rats.

First we move the Zombie in again for the assist.

Next the Wight comes in for the blitz.

Knocking the rat in the square is just as good as a knockback.

This leaves the Ghoul clear to make the attempt.

 

Assuming we just have the 1 reroll (this time from the Ghoul’s Dodge skill rather than a Team Reroll) we can see that we have just improved the chances of scoring from 39% to 61%. These are familiar success numbers, being the same as we saw above for the same-rank and 1-rank Loose Screen chances. What is happening here?

 

Connections

Let’s look at the screening as a combination of the simple analysis at the start of the article. We’ll draw lines over the pictures to represent the screens being formed.

This red line represents a loose screen same rank with a 39% chance of breaking through.

The orange line represents a loose screen 1 rank back with a 61% chance of breaking through.

 

Let’s now combine these to draw all screen combinations of this column defence:

We see that we have two ‘red line’ same rank Loose Screens, as well as a number of ‘orange line’ 1-rank Loose Screens backing it up. This formation is not only tough to break but has a lot of redundancy built in. Remove any one of the 6 players in this formation and we still get a red line spanning the formation.

The removal of the centre front defender leaves the same-rank screen intact.

 

Let’s revisit the last scenario with these lines drawn in:

The yellow line represents a Loose Screen 2-ranks with an 89% success chance.

 

We can immediately see the problem. On the space between the centre and left columns we only have one red line. This is between the rear left column rat, and the front centre column rat. Removal of either of these players (or even a push to disconnect them) will result in the removal of the red line. As the front centre rat is easier to target (i.e. get an assist on) this is the one that is blitzed.

This is why the chance of dodging through the screen improved from 39% to 61% in these two scenarios. We are swapping out a red line for an orange line when we go from a flat defence to this one.

 

Over-extended and Over-loaded

The column defence is the optimal setup of a more general rule than can be applied to your games. I call it “counting 3’s” because the principle is making sure that these screens are in place, and you can do that by counting 3 squares from a player to make sure that another player is present. The fewer diagonal squares you have to count the stronger the formation.

The idea behind “counting 3’s” is to improve your play by speeding up your calculation and helping you to spot mistakes before you make them. It will never be as good as actually calculating all the odds of all the screens that you are creating, but this calculation is hard to do, especially when under time pressure. Therefore we try and replace hard calculations with good-enough shortcuts.

Take this position – can you see the weak points?

Messy positions like this, which are common in the game, are much harder to fully calculate, and so mistakes can be made. But by “counting 3’s” we can pick out some issues. Here are some problem areas shown in purple:

The purple lines show players that are too far apart to form a screen.

 

We can quickly see that the Blitzer at the back (red stripe on base) is a bit of a problem. This player is trying to cover the centre but ends up not being in a great position to form a screen with either the left most or right most players. The result is that the screen with both sides is weak. This player is over-extended – by trying to do too many things they end up not doing either of them well.

Over-extended players are usually not the weak point of the formation, but the cause of the weak point. What this means is that another player in the defence has to pick up the slack of the over-extended player. This player is in a good position, and that means if they are removed the defence is a lot weaker. This vulnerable player is Overloaded. This makes them the weak point because if they are removed the defence collapses.

 

So which rat is overloaded? The centre rat of the front row might be a good candidate to check. As it is not being helped in forming a screen with the two rats farthest left by the rear-most Blitzer we can see that it has to take up the slack on the left side. However it is adequately supported by the other Blitzer who forms decent screens with the left most rats.

So although this front rat is important because the removal of him would result in the loss of the red lines, the player is not overloaded because the Blitzer to the left will pick up the slack caused. And you are not overloaded if you have another player helping out.

 

Rather the overloaded rat is the one two squares right of him.

The purple line is an orange line in strength, but highlighted purple to show the vulnerability.

 

We can see that this rat has a lot of important screens that he is a part of. But there is only one screen that is made from a player on the left of him to a player on the right of him. That means in screens that go through the column that this rat is on, he is a part of all of them but one (including ones he is connecting).

 

All of the redundancy in the defence on the right side of the formation is built into a single rat. This is why he is overloaded. There are 6 links that connects players to his left with players to his right, and he is part of 5 of them. 87% of the screens that cross his column go through him. It’s too much for a single player to be expected to handle. Maybe not so bad if he were a Mummy or Big Guy (until they bonehead of course!), but certainly too much for an St3, Av7, no skills player!

 

Compare that to the redundancy of the double column.

Each connection combination from left column to right column has a different colour to mark them out.

 

There are 8 paths that you can draw from the left column to the right column. Four of them go through the top centre rat and four of them go through the bottom centre rat. When we remove one of these rats the total number of paths drops to 4. Each rat in the middle is responsible for 50% of the screens that go through their rank. This means that neither of these centre rats are overloaded.

 

Future notes

It is worth noting at this point that whilst I have been speaking about screen strength purely in terms of being able to dodge through there are other things to think about. You’d not want to dodge through on the first turn, for example, even if it was quite easy. At this early stage of the game it is often about how much pressure the attacking side can put on your line. We’ll talk about this in a future article, because it uses the principles of screen strength, over-extended and overloaded players to discuss how to set good defences and how to attack them. But as a little teaser here’s a potential situation if that overloaded rat is knocked down and the Undead team pushes up into it rather than tries to dodge through.

The Mummies don’t have skill rings (mainly because their bases are too large!) but should be easy to spot due to their size.

 

You can see how the presence of the St5 players has allowed the Undead team to drive a wedge into the space created from knocking down the overloaded player and pushing hard into the over-extended player. Next time we’ll talk about tackle zones and assists and from that build up into analysing positions such as this.

 

Challenge!

Now you should be able to use our screening knowledge to look at this scenario. If you could adjust the position of any single player by just one square to strengthen the defence, which one would you move, and where would you move him to? I’ve put some grid markings in (columns noted A-J, rows noted 1-5) to help identify the players. Let me know as a reply on the forum, twitter, or wherever this has been shared!

 

 

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