Most browser football games, and the Classic mode in NextBall, keep the ball inside walls. The ball never goes out, nobody is ever offside and the game never stops. That makes matches fast, but it also means that the tactics of real football do not matter much.
Real Match takes the walls away. The ball can leave the pitch, the referee logic restarts play the way a real referee would, and the attacking team has to stay onside. You can play it as 3v3, 5v5 or a full 11v11 on stadiums built for each size, so the pitch always fits the number of players.