The scene all unfolded in Madison, Wisc. back on Nov. 8, after Del Rio had allegedly rammed his vehicle through a person's fence ... and then attempted to flee the area on foot.

Cops say they were able to catch up to the former NFL head coach on a street near the crash site -- and in a police report, officers wrote he reeked of booze.

In dash cam footage, you can hear he did admit to drinking "a little bit" earlier in the evening ... and after initially stating he had not been driving -- he did fess up a few minutes later to getting behind the wheel.

Cops put him in cuffs and threw him in the back of one of their rides -- and after they informed him he was under arrest for OWI, Del Rio became increasingly uncomfortable.

Police video shows he asked three separate times to use the bathroom ... at one point saying, "Please, just let us f***ing take a leak."

Minutes later -- as a cop waited for a search warrant for his blood sample following his refusal of a breathalyzer -- the former Raiders coach began to yell out in agony over and over again.

The cries grew so loud, Del Rio's arresting officer eventually asked, "Sir, what is going on?"

Del Rio replied, "it's just this pain."

When Del Rio and the officer ultimately arrived at a nearby medical facility for a blood draw -- Del Rio took several moments to get out of the car ... yelling that his "f***ing arm won't work." He was finally helped out of the vehicle after several seconds of struggling.

Del Rio had been working as an adviser on Luke Fickell's Wisconsin Badgers' staff at the time of the arrest ... though the 61-year-old resigned from the position a few days later.