"It's not planned," Matthews said. "I was going to hit him with the predator, and then I had a light bulb go off in my head. It's just having fun. We're a bunch of kids out there running around and having fun at each other's expense."

RELATED: See Clay Matthews' Off-Season Workout

For all of their on-field antics, Matthews and Kaepernick usually train together for at least part of the NFL off-season. In the final few weeks before training camp starts, they can usually be found at Proactive Sports Performance in Westlake Village, California.