Smith responded by pulling Jenkins to the ground by his facemask, and a brawl between the two sides followed. While tempers certainly run high on the football field, especially between two divisional rivals, grabbing and twisting a player's facemask, after the fact, is not only a stupid move but a dangerous one as well.
Granted, Smith isn't solely to blame for the fight that broke out after his touchdown, but he's clearly a primary instigator. At the same time, Jenkins had no business attempting a physical confrontation on Smith.
While Jenkins can surely be upset about the late-hit penalty, his vitriol should have been saved for his teammate Harper. Harper is the reason why the entire incident happened in the first place. Without the late hit, there's no reason for Smith to be angry; without Smith angry, Jenkins has no reason to approach him.
Ultimately, all parties involved in the fight are to blame. It was a cascading series of events, each one preventable, that compounded into the scrum we saw today.
Not just one player should be disciplined for the incident. Whether it's a fine, a suspension or a combination of the two, Smith, Harper and Jenkins should all be punished.