The description on TSA isn't quite accurate anymore, as of
This update it's now 25000 hits.
There's a massive bug in this game, where playing with a gamepad can randomly generate stats and unlock most of the cumulative achievements. (one-offs abd kill x in a match won't unlock this way)
Without that bug, this is just a grind, tapping left, right and holding down on the keyboard should get you the most hits with minimal effort.