New York Mets fan sparks outrage by throwing back home-run ball at Wrigley Field: 'Grow a spine'

A New York Mets fan behind enemy lines in Chicago has been slammed for giving into 'peer pressure' after throwing back a home-run ball at Wrigley Field.

The unidentified supporter, who was seen wearing a Mets hat and shirt in the outfield bleachers, initially celebrated after catching Francisco Alvarez's home run in the fifth inning of Saturday's game.

Yet to the dismay of New York commentators Steve Gelp and Ron Darling, he quickly gave up his souvenir after being urged by Cubs fans around him to throw the ball back onto the field.

'That is too much peer pressure,' Gelbs said. 'Grow a spine, man.'

Darling then added: 'Obviously, not a leader.'

It is tradition at many ballparks for home fans to throw balls hit into the crowd by the visiting team back onto the field as a way of protesting the runs they just conceded.

However, a supporter giving up the chance to keep his own team's home-run ball - even if on rival territory - is virtually unheard of.

Several users ripped into the Mets fan on social media, with one putting: 'Ban him from Citi Field.'

Another commented: 'Revoke his fandom'.

While a third said: 'Shame on him - He is NOT a true mets fan'.

Others even questioned whether the spectator was actually impersonating a Mets fan on the day with his hat and shirt.

'He's gotta be a Cubs fan who lost a bet... There's no other way,' one wrote.

Another posted: 'That’s not a Mets fan'.

While a third put: 'He must be an imposter in Mets clothing'.