Green’s Dictionary of Slang

to shoot; thus gatting, shooting, a shoot-out.

1920		A. Baer Speaking of Weddings 6 Aug. [synd. col.] A woman in Chicago gatted her husband to keep him at home.
1930		J. Lait Gangster Girl 129: I don’ wanna get you in no more gattin’ than what’s necessary, neither.
1995		L. Stavsky et al. A2Z.