When a batter has legs made out of jelly (normally an off-speed or curve ball heading at an unusual angle) and departs from a good batting stance. “His curve ball . . . it jelly-legs you.” - Phillies First Baseman Jim Thome, referring to Barry Zito's curve.
To hit the ball hard, typically used to refer to pulling the ball over the fence for a home run. "Derrek Lee jerked one of his patented doubles into the left-field corner to lead off the fourth against Minnesota lefty Johan Santana, the reigning Cy Young winner."
A player who is said to be juiced is thought to be taking performance-enhancing drugs. "It is now assumed, of course, that Bonds may well have been juiced on steroids at the time; the previous year he had set the all-time single-season record of 73 home runs, and his musculature was almost freakishly swollen."
A baseball that is said to be juiced is doctored or manufactured in some way that makes it travel farther when a batter hits it. "Spectacular increases in home runs have often raised the question: Has the ball been juiced up to travel farther, in order to increase the number of home runs?"
A fielder is said to get a good jump on the ball when he anticipates or reacts quickly to a batted ball and is thereby able to make a good play by fielding or catching it. Also see crack of the bat.
A baserunner gets a good jump when he is able to leave the base well before the pitch reaches the plate. "Upsetting the timing of the baserunner can effectively prevent him from getting a good jump.... Base runners often read a pitcher's look and get their jump, or start, based on the pattern the pitcher establishes."
breaking balls and knuckleballs, pitches that are difficult to hit due to movement rather than velocity. The term is also used to describe a "junk pitcher" or a junkball pitcher. "I couldn't believe he threw me a fastball because he had me down 1-2", Thames said. "He's usually a junk pitcher and he tried to sneak a fastball past me, and he left it up." See also: Eephus pitch
A pitcher who throws predominantly junk, usually due to a weak (or slow) fastball. A junkballer or a junk artist: "Like all junk artists, Trujillo will have to prove himself at the higher levels before getting a shot at a major league job." See also: Eephus pitch