[bluehair]

Sure, there are times when runner sees that he is dead meat and tries to run F2 even though F2 hadn't blocked access prior to receiving the ball. But there are also many times where F2 will set up blocking access to the plate before the ball arrives and when a runner sees access blocked, he decides to crash F2 (but if the base is accessible, there is no reason to crash F2).

Both cases happen.

If you are going to continue to allow F2 to block access without the ball, then even if you make a rule against it, you're going to keep having collisions with F2. If the objective is to prevent injury/concussions both sources of collisions should be outlawed.