The description for this achievement is misleading. It states you need 20 player kills in a single game but the medal in game states that you only need 15 player kills. Having just unlocked this last night I can confirm you only need 15 since I ended the match having killed the opposing player 17 times by the end of the match.
The achievement also pops up mid-game.
If you are boosting this (which I imagine you are since there is NO community) have the command points to 50, the resources set to 1000 and the respawn timer set to 0. Whoever is going for the achievement runs to the motorpool and captures that strategic point. Once captured, call in a tank and head to the entrance of the enemy camp. The other player needs to call in 2 of the cheapest jeep. Get into one of them and wait to be killed. Once you respawn hop into the other jeep but before being killed make sure to call in another jeep. Keep doing this until the end of the match (should take roughly 4:15) and the person not dying should receive this achievement along with 'Great Score' and 'Great Shooting'.
Then simply return the favor if needed.