Justin Gimelstob -- an ex-tennis star and current broadcaster -- plead not guilty to felony assault after he was accused of beating the hell out of a man during a trick-or-treating run on Halloween.
Gimelstob -- a former doubles champ who coaches tennis stud John Isner -- was arrested on the suspicion of roughing up a guy named Randall Kaplan while the man was trick-or-treating with his family in L.A. on Oct. 31.
In a restraining order Kaplan filed in November, he claims the tennis coach hit him from behind, pinned him down, punched him "more than 50 times" in the face and head and threatened to "f**king kill" him.