The player issuing the Scruffy may do so after any drive - good, bad or otherwise - but Scruffies are traditionally issued after poor drives. Scruffies are not automatic - that is, the other members of the group must agree to accept the challenge after it has been issued - so calling "Scruffy" after a great drive might not get you anywhere.
If the player calling Scruffy pars the hole, he wins the bet from those who accepted it; if he makes bogey or worse, he owes the players who accepted the bet the agreed upon amount. The Scruffy amount should be set before the round starts.

