Former NFL star Eddie Lacy is fortunate he didn't hurt himself or anyone else on the night of his DUI arrest last month ... 'cause cops claim he was driving around with a blood alcohol content level over FOUR TIMES the legal limit.

The Scottsdale Police Dept. says it all happened back on Sept. 30 ... after a woman dialed 911 and told dispatch that someone matching Lacy's Audi SUV description was driving so erratically, she was worried they were "going to kill somebody."

According to an SPD police report, obtained by TMZ Sports, cops pulled over Lacy in his Q8 a short time after the call was received ... and almost immediately, officers noticed something was off about the ex-Green Bay Packers tailback.

"Eddie's speech was slow," one cop wrote in the documents, "slurred and mumbled as soon as I began talking to him."

Body cam footage shows Lacy did appear to be having trouble formulating smooth and coherent sentences -- even after the officer told him he recognized him from his Alabama Crimson Tide playing days.

Lacy, though, was able to say he had just flown in from Green Bay and was on his way to his girlfriend's home -- which he stated repeatedly was just a few yards away.

But, when questioned further during the stop ... Lacy told one of the officers at the scene he had drunk on his flight into Arizona -- consuming "a single shot" of tequila.

Eventually, cops got Lacy out of his ride -- and while they weren't able to conduct a variety of field sobriety tests due to injuries Lacy said he suffered during his football career -- they did get him to blow into a breathalyzer ... which they said yielded a result of .325.

When asked if he knew what the legal limit was in Arizona, Lacy said yes ... pointing out, "I already had a DUI bad" in the past. However, Lacy then couldn't say whether or not .08 was the right number.

Cops then slapped the cuffs on the 34-year-old ... and told him he was arrested for DUI.

Court records show he's since been hit with several criminal charges -- including one count of extreme DUI BAC greater than or equal to .20. He's slated to face a judge for a hearing on the matter later next month.

As Lacy noted in the police video -- it's not the first time he's been arrested for extreme DUI ... police documents we obtained show in March 2022, he was accused of driving around Scottsdale with a BAC of .247.

Lacy -- who made an alumni appearance at Lambeau Field last month just days before his arrest -- logged snaps in the NFL from 2013 through 2017 ... piling up 3,614 rushing yards in 60 total games.