Appendix:Glossary of baseball jargon (J)

jack

 * A home run or to hit a home run. "Hitting a jack" or "Jacking one out of here."

jam

 * To pitch far enough inside that the batter is unable to extend while swinging. "The pitcher jammed the batter".  The batter was "handcuffed" or "shackled" by the pitch.
 * When runners are in scoring position with less than two outs and good hitters coming up. "The pitcher is in a jam."
 * "Bases are jammed" means "bases are full." There are runners on 1st, 2nd, and 3rd bases.

judy

 * A softly hit ball that goes over the infielders and lands in front of the outfielder for a hit. See blooper or Texas Leaguer.

Junior Circuit

 * The American League, so-called because it is the younger of the two major leagues.

junk

 * breaking balls and knuckleballs, pitches that are difficult to hit due to movement rather than velocity.

junkball pitcher

 * 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 minor shot at a major league job."