But keeping the tag is why the runner got off the base. If a coach was going to challenge it, he would say, "a normal quick tag wouldn't have taken him off the base...but keeping the tag on a player leaning in one direction did, because the added force witth the player's momentum was enough to move him."

The tag wasn't necessarily excessive, but definitely not needed, and was enough to change the outcome of the play...so THAT makes it excessive, because the player would have been safe and not fallen off the bag if the tag wasn't kept.

It's a tough call, especially in real time, but it also sets a precedent and will make other players tag, push, hold more aggressively in hopes it bumps a player off the bag, especially since there isn't a rule against it or penalizes the tagger. Why WOULDN'T they give a little extra push on each tag as long as it's not totally egregious.