Maybe the terms "stomped" and, especially, "kicked in the head" are a bit too strong (kind of like the characterization of Howard Dean's "scream" with the crowd at a political rally or saying Bill Clinton "wagged" his finger when denying sexual relations with Monica).   But Profitt clearly did more than just put his foot on Valle's shoulder.   He put his foot on her shoulder/neck area and forcefully shoved her shoulder down towards her head. In the video it seems apparent that enough force was used to possibly cause sprains or even perhaps a dislocated shoulder.
Valle was diagnoses with having both sprains and a concussion; the latter may well have resulted from her being tackled to the ground.

If Paul's security people thought that Valle's trying to put the "award" through the open car window was a threat, all they had to do was get between her and the car and/or hold her arms so that she couldn't do that. When the police or private security guards tackle someone, twist their arms, etc., just for some non-violent 'offense' such as carrying a sign or refusing to leave a rally, that's excessive force.