The ROK has conscripted national service and not all go to the military. A lot of the riot police are conscripts, but their leadership are career professionals.
Unlike US police who may be street cops, patrol officers etc., who are trained in civil disturbance ops and issued a helmet and shield for use as necessary, the KNP riot police are full time. When they're not actively working a civil disturbance, they are training for them. They'll show up in specially equipped busses that have the glass covered by fencing, tear gas, launchers, shotguns, etc. strapped inside. When they stand in formation, every 3rd or 4th one has a fire extinguisher strapped to his back.
They are incredibly efficient, and appropriately aggressive. They have no problem escalating force in response to a crowd. I once saw a demonstrator pitch a lit molotov cocktail at a formation of police. By some quirk, it did not shatter, but skidded along the asphalt coming to rest in front of the formation. One of the KNP picked it up and threw it right back into the crowd where it did shatter. They also seem to have a very large budget for tear gas, and little hesitation using it.
Nice!
South Korea has a long history of college students demonstrating pretty violently, throwing rocks and molotovs.
So the Intel folks routinely keep track of who are this year’s new ringleaders and bomb throwers. The kids are new to the game, but the nets are out for them by pros.
Then when they graduate, and have to do their National Service, those individuals are often funneled into the riot police, and put in the front rank, to be on the receiving side.
Yes there is poetic justice to that, but it also helps teach those kids a lesson, and helps them grow up into into better balanced citizens. Rehab for radicals.
I got a whiff of the tear gas on a business trip to Seoul once. The sight of riot troops standing in line with legs placed side to form a strong and menacing stance, each one holding an arm extended to steady his lexan shield, was quite impressive.