Rob Gronkowski got Red Sox fans fired up for their Patriots' Day game in the most Gronk way possible -- by spiking the ceremonial first pitch straight into the ground!
The New England Patriots legend took the mound at Fenway Park just before Boston took on the Guardians in the annual holiday tilt ... and instead of firing a fastball to his catcher, he decided to bring out his touchdown celebration instead.
Check out the footage, Gronk hurled the baseball into the dirt so hard, it made a loud thud -- and the crowd couldn't have loved it more!