the "bump" at first base

[tcannizzo]

This is always situational depending on the level of play.
The times I have seen this, I actually "warned" the runner and her coach, rather than the defense.

IMO, defense can commit OBS all day long, not my problem; but the offense has zero right to physically move the defender out of the way.

In extremely low-level rec, I have, on occasion, casually mentioned to the defensive coach that there is a an increased risk of collision/injury for those players who always have their foot on the base, when there is no throw coming in.