Ibrahim and Murat A, both 28, were accused of assault after they were caught up in an argument with laughing onlookers after one of them fell off his bicycle outside the Citysnack outlet in Leuven, a university city east of Brussels.
One of the brothers reacted angrily and punched one man while the other tried to hold him back, the Het Laatste Nieuws reported.
CCTV footage of the incident showed one of the brothers attacking the onlooker, but the brothers look so much alike that police nor the victim could reportedly tell them apart.
HLN reported that both brothers were taken in for questioning but only one of them showed up. That brother told authorities that he had only tried to stop his brother.
Police investigators determined that one of the brothers carried out the attack, but it was unclear exactly which one threw the punch.
"It's obvious that one of them actively tried to hold the other back. So he can't be judged as either perpetrator or accomplice," the judge was quoted as saying by HLN.