A Calgary constable on trial for aggravated assault never told his commanding officer he had punched the handcuffed man he was arresting four times before throwing him into the pavement, head first.

According to Sgt. Clint Grabowski, who testified at Const. Trevor Lindsay's aggravated assault trial on Tuesday, police protocol requires officers to fill out a use-of-force report if they become at all physical with someone.

Daniel Haworth suffered a fractured skull and brain bleed in May 2015.

When Lindsay called paramedics to respond to the parking lot of the arrest processing unit (APU), he said Haworth "needs EMS in a bad way."

Haworth was unconscious for about five minutes, and when paramedics arrived on scene, he was "bleeding profusely" from his nose.

Months after he was injured, Haworth died from a drug overdose.

Daniel Haworth suffered a fractured skull and brain bleed after his arrest by Const. Trevor Lindsay, who is now on trial for aggravated assault. (Court exhibit)

Handcuffed suspects vulnerable

The officer and his partner had arrested Haworth, who had been accused of stealing collectable coins from his ex-girlfriend. Haworth was drunk and agitated at the time.

Once police had transported him to the arrest processing unit (APU), Lindsay had Haworth pressed against his police car. Lindsay is accused of striking Haworth in the head, causing his face to bleed.

Lindsay told Grabowski, his supervising officer, that Haworth had tried to spit blood at him, which resulted in what the accused described as a "hard takedown."

Court of Queen's Bench Justice Michael Lema has been told by several witnesses that spitting at a police officer is considered a serious assault.

But Grabowski told prosecutor John Baharustani that when a subject is in handcuffs, they don't have ability to break a fall, so officers "have a duty to care" and should use "minimum force."

This graphic security footage shows what appears to be a Calgary police officer punching a man repeatedly before throwing him on the ground. 0:42

Grabowski also said it's much easier to control an arrestee who is handcuffed behind their backs and avoid being spat on because "they can turn their head all they want and they still won't be able to spit on me."

Lindsay and his partner had been told that Haworth had used heroin the night before.

Under cross-examination by defence lawyer Don MacLeod, Grabowski agreed this information would ramp up officers' concerns about having blood spat on them.

Lindsay's actions are not in question, rather, the case will come down to whether he exercised reasonable use of force or whether it was excessive.

Both Crown and defence will call their own use-of-force witnesses.

Lindsay is suspended with pay from the Calgary Police Service.