The Freshman - S4-E1
Corrected entry: At the end of the episode, when Buffy is fighting the vampires, she grabs a tennis racket, and just before she hits the vampire with it, the head of the racket flies off to the right of the screen and she continues to swing round and hit the vampire, running at her on the left of the screen, with the racket (minus the head).
Correction: That's not a mistake. All this proves is that even in the Buffyverse, tennis rackets can be poorly made.
Twotall