A nice fact here, this trophy can be easily earned with two people working in private matches which are very simple to create. Have one player enter the Multiplayer lobby and create a new closed lobby - it doesn't matter how easy or hard the password is, just so long as it's shared with the other player lol.
The other player then enters the lobby browser and hits the SQUARE button to join using the given password.
The host searches for the creator ChronicXBladePro for the featured map 'Shovel Dodgers 2' lasting for 15min and with a 200 kill limit. At the time of posting, it's the only featured map he's created.
Admittedly the trophy is unlikely to be popped in a single match regardless of the kill limit (due to respawn rates), but it's a very easy map to grind the kills on - think of a sealed dodgeball court (with no cover), only instead of a net there's a suicide drop, instead of a ball you're armed with an infinite supply of shovels, and it only takes a single hit to kill your target - aim with LT and throw with RT.
Just remember that the coding for the servers are a bit less boost-friendly than other games, seeing as how if one player is inactive for two minutes they're automatically disconnected from the match while the other is given a defeat, so both players have to be active for this to work.