No, there's no specific rule that he can't be out there. In fact, when a player is injured the coach can walk out onto the field. But this is a case where the refs should have used a some common sense and got him the fuck off the field or at the very least thrown a flag on him for instigating a scuffle.In short, whether Porter was on the field is irrelevant to the offsetting penalties discussion. He shouldn't have been there, by the rules, but there's no specific penalty for that - the fine that he will reportedly be issued is likely the right penalty for simply being on the field.
For one, even though coaches are allowed onto the field when a player is injured, why the fuck was Joey Porter a Linebackers coach out onto the field when one of the receivers is hurt? Not only that but, as the screen grabs and video show, Porter basically looks at Brown on the ground then wades back into a group of Bengal players bumps one of them then immediately starts talking shit to all of them.
Burfict is the dirtiest player in the NFL and PacMan Jones is a complete moron (as the Grammy comment shows up thread) but everyone needs to hold the officials to a much higher standard. They lost control of that game when they didn't flag Shazier/the Steelers sideline for celebrating concussing another player. That was the clear turning point of the game, when it started to look like there were going to be multiple fist fights between players. That was a terrible job of policing everything during that last sequence (I think Burfict should have been thrown out as he was clearly trying to hurt or fight anyone he could at that point, off setting flags on Porter and Jones and be done with it).
It leaves a really bad taste in my mouth that a playoff game was heavily decided by a call that involved a coach going onto the field under false pretenses, bumping a player, talking shit and somehow instigating a flag while he gets off scot free.
And if you don't believe Porter was going out there with the explicit intention of talking shit/causing a scuffle, it's been reported that he was rewarded the game ball. I am pretty sure that wasn't because of his excellent job at looking at a concussed Antonio Brown for 5 seconds