Sunday night's violence came as Irish republicans paraded near British Protestant districts of north Belfast. Such demonstrations, usually by the Protestant side, trigger riots every summer in Northern Ireland.
Police donning flame-retardent suits, helmets and shields spent nine hours standing their ground versus mobs of masked, hooded Protestants. More than 100 rioters threw bottles, bricks and fireworks at police lines until early Monday.
Police commander Matt Baggott says his officers demonstrated "courage and restraint."
Most of those hurt suffered cuts and bruises. Four officers were hospitalized with more serious injuries.
One suspected rioter, a 17-year-old boy, was arrested Monday morning.