It degenerates into players staying in zones and there's no movement. It starts with defenders unable to carry the ball up the field because if there's a turnover there's a striker poaching. Midfielders would become exhausted, because they'd be tasked with carrying the ball upfield but also getting all the way back and helping on defense. To stop this, defenders would stay in their third, midfielders in middle third with occasional forays up or back, and attackers would stay up high. The game would lose flow and movement.
In the late 60s, Ajax played AZ '67 in a game without offside, and other rules intended to bolster offense--kick-ins, and corner kicks being taken from the place the ball went over the end line, unless it was in the box. This game featured Johan Cruyff and it was said: "During the match, centre forward Johan Cruyff and winger Piet Keizer were reduced to goal-hanging, mostly in vain. “Most of the time he was of little use,” the reporter for the
Het Vrije Volk newspaper said of Cruyff. Which,
De Telegraaf newspaper reported, could hardly be blamed on Cruyff, for neither he nor Keizer was involved in play much by their teammates." The game was played with 2 30-minute halves and ended 2-1.
Also, here's a video of 2 German teams trying. The box became much more congested, the game was less structured, and the final score was 1-0.
View: https://www.youtube.com/watch?v=reY1CWMo57Y
