The Collaborative International Dictionary of English v.0.48:
frag \frag\ (fr[a^]g), v. t. [imp. & p. p. fragged (fr[a^]gd);
p. pr. & vb. n. fragging.] [by shortening from
fragmentation grenade; ca. 1965.] (Mil.)
To assault, especially to kill or wound, with a fragmentation
Note: This term became popularized when disaffected American
troops serving in Vietnam were reported on occasion to
kill unpopular commanders by the use of grenades.
The Jargon File (version 4.4.7, 29 Dec 2003):
[from Vietnam-era U.S. military slang via the games Doom and Quake]
1. To kill another player's avatar in a multiuser game. ?I hold the
office Quake record with 40 frags.?
2. To completely ruin something. ?Forget that power supply, the lightning
strike fragged it.? See also gib.