What actually happens in Coach Carter:
Coach Carter: I end up taking a road trip to the suburbs where I find my drunk ass point guard on top of Daddy's little princess!
Worm: Actually, I was on the bottom, coach. She was on the top.
Coach Carter: Worm, you want to be on the team? Because you're about six words from getting kicked off and kicked off this goddamn bus!
Carter is telling Worm to shut up, because what he just said made things worse. Six is an arbitrary small number, just making the point that Worm is very close to being thrown out of the team. Anything Worm says at this point could be enough to make the coach drop him.
Edit: just to be completely clear, this phrase isn't talking about six literal words, just that it would take dangerously little carelessness on Worm's part to get himself dropped. The general idiom is "N words from undesirable consequence" or "N words away from undesirable consequence", where almost any small number will do for N.
"You are are two words from getting thumped here!"
In the right circumstances the threat can be implied rather than specific:
"One word. Just one word."
The meaning is very similar to the saying, "When in a hole, stop digging." The speaker is generally angry with the person being spoken to, and nothing that person can say with make things any better right now.