The sports media universe is reveling in Green Bay Packers linebacker Clay Matthews‘ trouncing and trolling of San Francisco 49ers quarterback Colin Kaepernick during the Pack’s 17-3 win yesterday. Matthews striking Kap’s signature biceps-kiss pose after sacking him for a loss seems like serious taunting, but Matthews was the first to say it was all in good fun.

“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.

At Proactive, the two NFL stars follow the pre-season training schedule drawn up by Ryan Capretta and his staff. Matthews, who grew up nearby, has been working with Capretta for years. Kaepernick began training there after he turned pro.

After a workout prior to the 2014 season, Kaepernick told STACK, “[Proactive is] one of the best spots that I’ve been to, and that’s why I come back every summer. The workouts are tough. The training fits perfectly with my preparation for the season as far as I want to be a speed guy, I want to be someone that’s able to do things over and over and not get tired. The workouts are based on doing as much of the weights as you can and moving on to the next drill with very little rest.”

RELATED: See the full workout Colin Kaepernick performed at Proactive

During the training session STACK attended, Kaepernick and Matthews worked together on more than one drill. They also endured the same grueling core circuit at the end. All of which showed that, even when players appear to be enemies on the field, they can be friends (or at least friendly) while training off of it.