Dashcam video shows Bryce Masters tasered and dropped by police officer

A dashcam video showing a US teenager being dropped on the floor by a police officer has been "unsealed" by a US judge.

Seventeen-year-old Bryce Masters was stopped while driving to a friend's house to play Xbox in 2014.

In the video, Missouri policeman Timothy Runnels is seen tasering the teenager before dragging him along the road.

The footage shows him and letting Bryce fall on his face on the concrete.

It has been used in court where the 32-year-old former officer pleaded guilty to one count of using excessive force.

He has been sentenced to a four-year jail term, which begins in August, according to US media.

Bryce is seen in distress during the exchange which took place in Kansas City.

After stopping the teenager, the officer is seen approaching the vehicle on the right hand side.

After asking Bryce to wind down his window fully, he walks to the left of the car and opens the door.

Bryce is heard repeatedly asking the officer "Am I under arrest?"

Runnels asks him "Do you really want to get tasered?" before firing the weapon.

Bryce is able to exit the vehicle as he is continually tasered and follow instructions to lie on the ground, where he is then handcuffed.

Runnels then drags him to the rear of the vehicle and drops him, face-first, onto the concrete.

Bryce is then heard groaning in pain as he is then searched.

Warning: This video contains violence

See the video here. It contains violent footage.

The court case was brought to trial by the US Justice Department after local authorities chose not to prosecute Timothy Runnels for the incident.

He claimed at the time that he smelled marijuana on the teenager and that he was being uncooperative after being stopped.

He told the court he was "deeply remorseful" about the incident.

"At no point did I intend to hurt him, but I did," he said.

This image claims to show Bryce in hospital after the arrest

During the hearing in May, Bryce told a Kansas City court how the incident had affected him and changed his behaviour.

"People tell me I'm different. I feel different," he said.

"I get in the car to go somewhere and then I'll forget where I was going."

"I've missed job interviews because I forgot them.

"I feel physically and mentally weak every day when I get out of bed."

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