Ugly scene during the UEFA Europa Conference League final on Wednesday ... soccer star Cristiano Biraghi was pelted with trash while on the field -- and one of the objects hit him so flush, it opened a gnarly wound on his head.
The incident happened during the first half of West Ham's heated tilt with Fiorentina at Fortuna Arena in Prague ... after Biraghi's Fiorentina squad was awarded a corner kick.
You can see in footage from the game's broadcast, West Ham supporters were so upset over the call -- they launched empty cups at Biraghi's head.