The 'Rollercoaster' singer "had a few stern words" for the unknown prankster when he struck after Bruce Springsteen's closing set on Sunday (June 24).
© PA Images / Jonathan Short/AP
"The man was showing off to his mates after they were laughing at Ronan for being small," a source told The Sun.
"He always assumed Ronan was a lot taller and caught him unawares by lifting him up in the air for a prank.
"Not surprisingly Ronan wasn't happy at first and had a few stern words. After the punter was carted off by security, he saw the funny side. He always thought he was average height."
A spokesperson added: "Ronan was accosted by a man who was very drunk at a bar backstage. The guy picked him up and he was removed from the area by security."
Keating recently confessed that he was "s**tting [him]self" about making his acting debut in musical comedy Goddess.
The star is currently in the process of separating from his wife of 14 years Yvonne.
