One of two Prince George's County police officers on trial for beating a University of Maryland student in 2010 testified Wednesday that he acted because he perceived the 21-year-old as a threat.

Reginald Baker said he had already spent time clearing students from the streets following the Maryland men's basketball team's upset victory over Duke on March 3, 2010, when he saw John McKenna move quickly toward mounted police with clenched fists, not obeying officers' commands.

"I thought he wasn't going to stop," Baker said. "I knew I had to get to him before he got to the horses."

Baker said he moved toward McKenna, yelling, "Get down, get down, get down, get down, get down," before engaging the student with his shield. Once McKenna was on the ground, Baker told McKenna to open his hands -- not knowing what might be in them -- while striking him with a baton to release his fists. He acted out his motions in court, wearing a helmet and holding a shield and a baton.

McKenna suffered injuries to his head, wrist and arm. The prosecution contends that Baker and James Harrison, who also struck McKenna when he was on the ground, abused their power and used unreasonable force during the incident.

Baker and Harrison are charged with second-degree assault and misconduct in office. Prince George's County Circuit Court Judge Beverly Woodard on Wednesday granted a defense motion to dismiss the first-degree assault charges against them.

Woodard said there was not enough evidence to prove that McKenna's injuries were both serious and permanent. She also noted that a prosecution expert saw officers striking McKenna's body but not his head.

Prosecutor Joe Ruddy said that McKenna suffered a concussion, which could lead to additional issues down the line. But Woodard said the prosecution didn't present evidence that McKenna hadn't recovered from his injuries.

The second-degree assault charge carries a maximum penalty of 10 years in prison. State's Attorney's Office spokesman John Erzen said there is no set sentence for the misconduct in office charge, as long as it is not "cruel and unusual."