Trip Attack

From publisher blurb:

Like the attack of opportunity, the trip attack is often ignored or underutilized in many d20 games. Many gamers find its value somewhat dubious, choosing instead to focus on other aspects of combat with more immediately obvious benefits. Even among those who do make use of trip attacks, many only bother in dire circumstances, almost as a last resort. This, however, means that many gaming troupes miss out on a very rewarding part of the d20 system. There are a number of potential ways one might use a trip attack to better his or her situation. From a tactical standpoint, the trip attack need not always preempt one’s own defeat. It can be quite useful in “pushing” combat encounters in a favorable direction.