Something similar happened during a televised football game late last year. It turned out that the incident was due to the security crew dousing a couple of guys (who were brawling in the stands) with pepper spray. Caused a bit of a commotion across the airwaves, that's for sure.
Anyway, I heard from another source that the noxious fumes were mace. Whether it was released by security or some random goofball remains to be seen.
-Jay