I'll take a relatively broad view of it when resolving. Throwing a punch is obviously sufficient, but tackling, shoving someone hard (such that they fall to the ground or come close to it), or other similar physical attacks will count.

It doesn't have to be two-sided, it's enough if just one person throws a punch or tackles someone.

It will only count if it happens in the US Capitol Building. Offsite altercations don't count. And it needs to be between two congresspeople - a congressperson assaulting an aide doesn't count. But I WILL count it if it happens outside of a formal session of congress, like in the hallway or something, or a committee meeting, or anything else that goes on in the Capitol Building.