Last night Highlander and I must have played a series of home run derby competitions in ESPN Baseball for close to an hour. You basically line up side by side and you each get a pitcher that throws easy down the middle pitches to you. The time limit can be 2 - 5 minutes and you get points for calling where your homerun will go, which zones you "own" by being the last to hit a homer in the area and a bonus for having the longest homer in the session. The main way to get points is to simply hit home runs of course.
You also have to manage your batter's stamina bar, if you keep hitting "B" for power swings you'll get tired. You have to alternate with "A" contact swings to stay consistent.
It was a real blast and if you're looking to kill 20 minutes and don't want to get tied up in a full game it's a fun way to play. The only down side is you need to re-create the game after every round thanks to their stupid auto-disconnect crap. That only takes 30 seconds to do though.