Hmm... but surely playing dirty is half the fun of blood bowl? After all, the Bright Crusaders will always stay in mid-table position 'until they shape up and learn to play dirty!'
While it's possible to argue that the
'Effective punishment of a foul is next to nothing'
It's equally valid to argue that one ought to factor in how useful the foul is likely to be. After all, it's very rare that a player is all alone and surrounded by enemy players - even if they are, that means that the rest of your players have pretty much a clear pitch in which to score.
Thus, most players are pretty safe from a foul.
It's fairly rare for a player to have more than +3 to a foul attempt, so on a fairly average player (say a human lineman), the fouler needs to roll six or more on two dice -slightly better than even chances. Then, he's got slightly better than even chances of knocking the palyer out for the drive/game. I really don't think that the effort of causing a foul is worth the risk of leaving your endzone less well-defended.
Even if you put in a catcher instead, you're more likely to get through armour but only equally likely to hurt them. Against Big Guys, who in my experience get more than their fair share of fouls inflicted on them, the risk is even higher, since you need more players to increase your chances to anywhere near high enough to pay off.
So, to look back on your equation, we ought to write:
Usefulness of a foul = (Potential damage - risk taken)/Effective punishment.
I also disagree that the punishment of a player sent off is only for one drive - unless the coach has specifically worked into his strategy players being sent off, his reserves are needed to replace hurt players. If he has taken this into consideration, the 1/2 chance of being sent off for multiple fouls is enough deterrent - few rookie coaches have many reserves, and veteran coaches with multiple reserves are more likely to take casualties because they're playing tougher opponents (In the vast majority of cases).
While it's impossible to quantify potential damage and risk taken, I think most of us would agree that it's pretty rare that you're going to gain much from committing a foul except keeping up a grand old tradition of the game!
Nevertheless, thanks for the considered answer!
- then weres the harm in giving him a quick kick in the head as you run by. 
