The Polish President was at a memorial dedicated to Poles killed by Ukranian insurgents in 1943 when the incident occurred.
The visit has been unpopular among Ukrainian nationalists who see the insurgents as freedom fighters.
The suspect has now been detained by the authorities and faces charges of hooliganism and could be put in prison for up to three years.
Mr Komorowski has joined a long list of other politicians who have found themselves the unsuspecting targets of various missiles.
Earlier this year a sandwich was hurled at former Australian Premier Julia Gillard.
Source: The Independent