"And Vaisey off too, he’s their best goal-scorer...."
-- Ron Weasley (HBP14)
Vaisey is a Chaser on the Slytherin Quidditch team in 1996 and is considered to be their best goal-scorer that season. A Bludger hit him in the head during a practice session, so he was unable to play in their match against Gryffindor (HBP14).
High goal-scoring Quidditch Chaser
Vaisey derives from the Anglo-Norman-French word enveisie ("playful, merry") and comes from Old French envoisie ("to sport, enjoy oneself") (Internet Surname Database).
Vaisey is no more than a year older than Harry, since he was on the team in Harry's sixth year. As he hadn't appeared before, he could therefore be younger than Harry.
Lexicon list of Chasers