What made Leo Messi do this?

Lionel Messi and Mapou Yanga-Mbiwa both received yellow cards after a heated exchange that saw the Barcelona No. 10 head-butt and grab the throat of the Roma defender in a 3-0 friendly win for Barca in the Joan Gamper Trophy match on Wednesday.

It's unclear what provoked the incident, but in the 34th minute Messi and Yanga-Mbiwa came face-to-face, with the Argentine clearly upset about something. Yanga-Mbiwa appeared to initiate the contact, leaning in with his forehead, and Messi responded by head-butting the French defender and then reaching for his throat.

The two players walked away of their own volition, with both receiving yellow cards. The offense could have easily drawn red for both, but Spanish referee Javier Estrada Fernandez instead only issued yellow.

Messi scored seven minutes later to give Barcelona a 2-0 advantage, building on a 26th minute goal from Neymar.

Ivan Rakitic left no doubt as to the outcome with a 66th minute strike from long range for the 3-0 final.

Roma's Alessandro Florenzi and Radja Nainggolan were also booked on a frustrating night for the visitors from Serie A.