Albert Haynesworth -- DUMPS WATER ON TRANSIENT ... Stop Harassing My Customers!

Former NFL superstar Albert Haynesworth dumped a bucket of ice cold water on a transient who posted up in front of his burger joint ... after the guy allegedly harassed several female patrons ... and TMZ Sports has the footage.

Haynesworth -- who famously signed a $100 million contract with the Redskins in 2009 -- now owns the BurgerFi restaurant in Knoxville, TN ... right near the University of Tennessee campus.

Haynesworth tells TMZ Sports ... he recently noticed a homeless man set up camp in restaurant's underground parking garage and called police to escort him off the property.

But according to Albert, the guy came back --and began harassing Haynesworth's patrons.

"He swung at some girls.The guy was running off customers."

So Albert decided to take matters into his own hands -- "I gave him the ice bucket challenge!"

Albert says he took a bucket of water from the ice cream machine and doused the guy ... hoping it would send a message that he wasn't welcome on the property.

"I don't usually care [about homeless people on the property] as long as they don't mess with people and sometimes we’ll make them food when they come up to the front and give out forks and napkins to the customers."