10:10 AM PT -- Law enforcement tells us Incognito was placed on an involuntary psychiatric hold to be evaluated. It's essentially the equivalent of a 5150 in California. It's technically not an arrest -- but a forced mental evaluation.

It's not the first time Incognito has been placed on an involuntary psych hold -- the same thing happened a few years ago in the wake of the Jonathan Martin bullying scandal.

Richie Incognito was involved in an altercation with another man at an upscale Florida gym -- with the alleged victim claiming Incognito threw a dumbbell at him ... and cops were called.

Multiple sources tell TMZ Sports .. the 4-time Pro Bowl lineman was working out early Wednesday morning when he got into it with another guy who was working out.

We spoke with the alleged victim who tells us Incognito first threw a tennis ball at him for no reason -- before grabbing a dumbbell and heaving that as well.

The alleged victim says Incognito was rambling about the government and screaming at the man to "get off my f*cking playground."

Law enforcement confirms cops were called to the gym and met with Incognito.

Multiple gym sources say Incognito was taken away by police -- but cops won't say if he was formally arrested.

We've attempted to contact Incognito for comment -- but so far, no luck.

The 34-year-old has had a turbulent year -- back in February, his old Miami Dolphins teammate, Jonathan Martin, was arrested after posting a gun threat directed at Incognito and others.

Incognito then suddenly announced his retirement from the NFL while still under contract with the Buffalo Bills. Just this week, the Bills essentially granted him his release so Incognito could resume his NFL career with another team.