You must beat an entire Contractions game for this achievement (all 20 waves). You don't need a team of 3 or 4 to complete this achievement, but having more than one player will definitely help. Contractions has a set spawn rate regardless of how big your team is. A single player will have to fight against the same amount of enemies a 4 player team would. Now with that in mind, teamwork is essential to this. A solid method for this is playing on "Mechanized Invasion" and be sure each person understands their role.
See "Handle with Care" for additional information.