# cbloom rants

## 1/25/2004

### 01-25-04

Most coaches and sports analysists really have no concept of game play study and theory. For that matter, most people who make and play games don't. Let me consider a simple typical case from the game I'm playing these days, Rugby. The correct way to analyze decisions in a game like this is using probability and EV (Expected Value). In Rugby you are constantly running with the ball and you must decide whether you should keep it or pass. Let's examine. Say if you keep it, you have a 10% chance of scoring, a 50% chance of being tackled and keeping possesion, and 40% chance of being tackled and losing possession. If you pass, the guy will have a 20% chance of scoring, 40 of keeping possessions and 40 of losing. However, your pass has a 75% chance of completing, a 20% chance of being dropped or knocking on for loss of posession, and a 5% chance of an interception for a catastrophic turnover. Now we must assign values to each of these. For concreteness, let's say - scoring is 100 value, keeping possession is 0, losing possession is -10, and interception is -50. So what's the EV of each move? Holding the ball is : 100*.1 + 0*0.5 + -10*0.4 = 10-4 = 6 ; If the pass is made the EV is 100*.2 - 4 = 16. The EV of the pass, however, is 15*0.75 - 10*.2 - 50*.05 = 6.75 ; we see the pass is very slightly better than holding the ball. The main thing this illustrates is all the factors and how delicate they are. For example, if one of you is a bad thrower or bad catacher, that probably throws the balance to where keeping the ball is better. Similarly, if they are in no position to intercept, that makes the pass much higher EV, so even if your catching and throwing aren't the greatest, it's probably worth it.

Another type of analysis that's completely missing from sport is the sort of thinking you have in poker - whenever you make a move that makes them feel sick, that's probably a good move. Similarly the concept of exploiting their weaknesses and playing to your own strengths, I almost never see people or teams do this.