an armed soldier or police officer whose job is to find snipers (= people who shoot at other people from hidden places) and prevent them from killing people

There were countersnipers on the rooftops monitoring the whole area. 屋顶上有反狙击手监视着整个地区。

Counter-sniper teams are selected from among the best marksmen in the police service. 反狙击组是从现役警方的神枪手中挑选出来的。