Even experienced players can get confused (or forget) when it comes to opener's jumpshifts and reverses.
Opener's Jumpshift into a (new) suit is GF. A jump shift is a skip of level and a change of suit. That means a really big hand. Responder cannot pass and the partnership cannot stop below game. The range is roughly 18+ (maybe 19+) points (counting useful distribution*).
Here are all of opener's possible jumpshifts into a new suit: