Valve actually implemented competitive multiplayer in Portal 2 but abandoned the mode because it swapped puzzle-solving for what quickly became "chaos".
Portal 2 writer Erik Wolpaw told 1UP that the multiplayer was kind of like Speedball with portals and, basically, didn't work.
"Along with co-op, [we had] the idea of sort of a competitive Portal multiplayer. We went down that path, actually, for a little while and had something up and running," he said.
"The best way to describe it is sort of Speedball meets Portal. You know, a sports analog."
Wolpaw went on to detail the "sport" saying that there actually was a ball that you had to move from one end of the play space to another.
The ball could be thrown but you mainly moved it by manipulating your portals to get where you needed to go in the quickest time possible.
Other players were trying to stop you by throwing portals in your path sending, well, anywhere else.
"It quickly became apparent that while it's fun for about two seconds to drop portals under people and things like that, it quickly just devolves into pure chaos," Wolpaw conceeded.
"It lost a lot of the stuff that was really entertaining about Portal, which was puzzle-solving. Cooperative puzzle-solving was just a much more rewarding path."
You can watch that discussion and others with the Portal 2 team at Valve in the video below:
A Portal 2 co-op video emerged over the weekend and demonstrated how players might go about solving puzzles together.