Play video content EXCLUSIVE FEBRUARY 2018 Law Offices of John M. Phillips

Warren Sapp didn't see this coming!!!!

The NFL Hall of Famer got SERVED with a lawsuit in his battery case by a process server PRETENDING TO BE A FAN ... and executed the trick play to perfection!

As we previously reported, Sapp is being sued by a woman who claims Sapp drunkenly bowled her over at a 2015 Super Bowl party in Arizona. She claims she suffered major injuries as a result.

The woman's attorneys had been trying to serve Sapp for more than a year but couldn't quite track him down -- they felt he was "actively avoiding the process server."

So, they sent a guy to a Sapp autograph session he had been promoting, hoping Warren would show up -- and they could finally slap him with the complaint and summons to appear in court.

The plan worked to perfection ... an unsuspecting Sapp even put his arm around the guy to pose for a photo before he dropped the bomb on him.