Worm burner is a multi-sport term that can apply to both golf and baseball. The use of the term is a criticism for one sport and more of a compliment in the other. It describes the same action in both circumstances, however.
The term, when used in baseball, describes a hard hit ground ball that scorches through the infield grass. It doesn’t take a big hitter like David Ortiz or Josh Donaldson to hit a worm burner. Solid contact with the right downward trajectory by any hitter can result in a ground ball classified as a worm burner.
Most pitchers like to induce more ground balls than fly balls, but a worm burner indicates a hard hit ball, despite that it was on ground level right off the bat. Give up too many of those types of hits, and it will be a long day on the mound regardless.
In the .gif file, Jose Reyes is facing Cliff Lee. It is hard to see the exact path of the ball, but it gets past third baseman Placido Polanco. This play may be routine if Polanco is playing at regular depth, but he was up towards the cut of the grass defending against a bunt. The change in the defense resulted in the hit playing as a harder hit ball on Polanco. There may be an asterisk next to the hit being classified as a worm burner, but it is still a good example.
On the flip side from the defender’s point of view, a worm burner can also be a good thing; there is less time to react and overthink a ground ball. Sometimes the in-between hops can fool an infielder or lead to bad hops. A hard hit ground ball means the fielder has to get set, put his glove out, and let the ball find the pocket. It is more catching the ball than fielding the ball.
The other sport that uses the term worm burner is golf. This refers to a ball that has the same action as in baseball and rolls quickly along the grass. Of course, in golf, the ball is supposed to go airborne all the time except when putting. Any ball that is rolling from the tee box to the green is not a good thing.
A worm burner is a hard hit ground ball that wakes up any worms lying below the surface of the grass. Pretty self-explanatory and very exciting to see live at a game.