Interesting thought...
Should the coaches NEED to tell their players when to back off? As Varsity athletes, we are (I lie...we SHOULD BE) mature enough to know when it's time to back off. I'm all for making restrictions (i.e. 3-touch-rule, must score off of a cross/one-touch, etc.) but should a coach need to tell a team that before it'll happen?
I'm not saying players should up and decide how they are going to play the game, but when it gets to be 8-0, 9-0, 10-0, there really is no point in continuing to run up a score. It's not hard to take a couple of shots at the keeper or let a defender challenge you instead of just flying past--I've done both. (I've also been whupped-up on 0-9...but we won't talk about that.

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I don't think a coach should have to tell his/her players when to back off, they should be able to determine that for themselves. A coach has every right to do as he/her wishes (in this case, in terms of restrictions and the number of players on the field) but as players, we should also see when it's time to backoff and act upon that.
Just an opinion.