According to "Half Life Wiki" -Overwatch Soldiers, known as Combine Soldiers by Citizens, and Stabilization Teams by the Overwatch Voice, are the basic transhuman infantry units of the Combine Overwatch, and the primary military of the Combine on Earth. In contrast to Civil Protection, whose duties are to enforce order within suppressed population centers, Overwatch soldiers are tasked with more hazardous actions requiring skill and tactic: from patrolling the treacherous borders of Combine-controlled territory to raiding Resistance-held strongholds and neutralizing any form of threat to the Combine.
Being the Combine military personnel, Overwatch Soldiers are given access to military-grade equipment and trained (or, more accurately, programmed) with advanced tactical combat training, making them more formidable strong opponents.