By Antony Clements-Thrower & Jackie Grant & John-Paul Clark A bar manager was hit in the head with a bottle of prosecco when two rival groups of football fans clashed after a joke posted on social media backfired. Fans of Scottish Premiership sideSt Johnstone were in Airdrie for their cup clash with Airdrieonians on Sunday afternoon. Ahead of the game violence broke out at the West End Bar where two groups of supporters clashed. Shocking video captured people fighting outside the bar before one yob threw bottles of drink back inside, with one of them striking manager Scott Rae. The fans, most …