BRUSSELS—Tens of thousands of people protested in Brussels on Sunday against COVID-19 restrictions, some clashing with police who fired water cannon and tear gas to disperse them near the European Commission’s headquarters. The rally drew about 50,000 people, Belgian police said. It was peaceful at first as protesters chanted and filled streets, waving placards and balloons with slogans like: “We want to be free again” and “No COVID slave ticket,” a reference to vaccine passes required for certain activities. Trouble flared later, with a building housing the European diplomatic service and a sandwich shop broken into, a Reuters journalist said. Police said more than 60 people were arrested, with three officers and 12 demonstrators taken to hospital. Belgium announced a slight easing of coronavirus restrictions on Friday despite record infections, but also said people must have booster shots after five months to keep passes for bars, cinemas, and many other …