A bench-clearing brawl occurs when players and members of the coaching staff not involved in the play leave the confines of the dugout or bullpen to partake in a fight between players of the two opposite teams that has started on the field. The most common circumstances for such a brawl is a player charging the mound (usually as the result of a perceived bean ball) or following a collision on the basepaths.
While most such brawls mainly involve a lot of pulling and grabbing accompanied by dirty looks, with few actual punches being thrown, they can sometimes lead to injuries, especially if there is a pile-up of players around the original fight. It is often not the players who started the fray who get injured, but otherwise uninvolved parties who join in. In rare cases, participants will use pieces of equipment as weapons, and this is much more dangerous.
Leagues do not look kindly upon such occurrences, and they usually result in a number of ejections, fines and suspensions. Umpires will usually attempt to defuse the situation and break up the most serious fights, but in such a situation they are outnumbered and often powerless. In particularly serious cases, spectators also get involved and civil authorities have to be called in to restore order.