A tradition unlike any other turned into a pain unlike any other for Rory McIlroy's dad at The Masters on Thursday ... 'cause the dude got drilled in the leg by one of his son's wayward shots!!
The surreal moment all went down on the 7th hole of McIlroy's opening round ... when the golf superstar tried to bend a shot around a tree to hit the green from the rough.
The problem? McIlroy's approach never turned -- and it made a beeline right for his dad!