Illegal screen or good offense

[gjacknow]

I have had this come up a number of times and can't seem to find the rule to address the situation.

basically a player with the ball is dribbling and another offenseive player gets in the way of the defense while moving but not while attempting to screen for nis team.

I have seen this happen when a player brings the ball up and dribble past a slower movnig teammate. If the defender forces the issue and runs into the ball handlers teammate, is it a foul?

Also on the fast break where a teammate is runnnig with him but the defender is trying to on the other side of that teammate and is blocked from takinig the shortest path to the man with the ball. (yes he runs into him while trying to get there, this is all while on the fast break)

Thoughts on what rules apply and the right call?

Thanks,

Greg J