It's ill-mannered, uncultured people, may be close to crime (this word based on name for homeless teenagers, which lived in Государственное общество призора (ГОП) -- it's kinda state shelter in St.Petersberg (not nowadays, but in the 20th century)) https://en.wikipedia.org/wiki/Gopnik :) tracksuits are suitable and not only Russian like it, for example, korean idols like it too: https://i.pinimg.com/736x/63/04/25/6304252e842808ea10b27bf5240cf6fe.jpg

Гопник -is bad guy

Not all Russians love tracksuits =) But gopniks love them because they're cheap and suitable for "life on the streets" where at any moment you may need to run or fight.

a policeman

Gopnik-slang Word of the Russian language, denoting the representatives of the urban stratum of low social status, poorly educated and without moral values, consisting of aggressive-minded youth (teenagers)