Things got heated during the 49ers vs. Lions matchup on "Monday Night Football" ... when San Francisco receiver Jauan Jennings got in a scuffle with multiple Detroit defensive stars -- which ended with him getting shoved into the stands.
The wild moment went down during the first possession of the contest ... when Jennings was tasked with blocking Lions corner Terrion Arnold in the end zone -- and it's safe to say he understood the assignment.
Jennings continued to defend Arnold even after their momentum moved them out of bounds .