[YMTC] Red robot on blue bridge

[Grim Tuesday]

This situation actually happened at the Queen City Regional last week, and I think there's an interesting discussion to be had about it. If I make a mistake in describing it, please correct me.

The blue alliance is attempting to triple balance. They have two robots on the bridge and the third one is making their way towards it. A red robot is defending the third robot from getting onto the bridge, and in the process, they are pushed onto the bridge through the actions of the third blue robot attemping to get on.

What penalties should the defending red robot receive? Are they interfering with the act of balancing? Are they being forced to interfere and therefore not penalized? If they aren't, at which point would they be? You make the call.

EDIT: Never posted in this subforum before; didn't know it automatically titled it. If a mod could correct my title, that would be much appreciated.