Colts' Darius Leonard's Mom Loses Her Mind Over New Car Gift!

Forget Rookie of the Year ... Darius Leonard is now the Son of the Year -- 'cause the Colts superstar just bought his mom a new car ... AND SHE FREAKIN' LOVED IT!!!

Leonard surprised his mom with a new Mercedes over the weekend ... and her reaction to the gift was priceless -- doing a FULL SPRINT to the car, followed by celebratory laps in the parking lot.

It's an amazing video.

"Ain't [nothing] like putting a smile on your mother face!" Leonard wrote of the present ... "We've been through so much and now it's like we're on top of the world!"

It's been an incredible year for Darius ... the 2nd-round pick came outta nowhere to become one of the league's best linebackers -- winning Rookie of the Year honors this month.

But, things are about to get WAY better for Leonard and his mom soon ... dude is now just 3 years away from a FAT new contract.