Brom and Ichabod both want to marry the lovely and wealthy Katrina. Brom realizes they are rivals and itches to fight it out openly with Ichabod, the winner taking Katrina. Ichabod, skinny and weaker than the tall, broad, muscular Brom, naturally evades that kind of battle. As the narrator puts it, this avoidance of battle ("pacific system") is very irritating ("provoking") to Brom:
There was something extremely provoking in this obstinately pacific system; it left Brom no alternative but to draw upon the funds of rustic waggery in his disposition, and to play off boorish practical jokes upon his rival.
Brom, therefore, gets together with his "gang" and they play the following "practical jokes" on Ichabod Crane:
They stop up the chimney and smoke out his singing school.
They break into his school at night and ransack it (turn it "topsy-turvy").
Brom teases ("ridicules") Crane in front of Katrina and teaches his dog to whine when he sees Crane.
Finally, Brom fakes up the "headless horsemen" and terrifies Crane into running away and not coming back.
Brom is popular, robust, and the "hero" of the piece, but he comes across as a bully. We wonder how Katrina will fare with him as a husband.