Developer Alibek Omarev has ported Counter-Strike 1.6 based Android version and you can grab the APK here. The game is a bit cranky to be paid on Android smartphone or tablet as you might expect. Omarev’s APK has the Counter-Strike screen littered with touchscreen controls which are fully customisable.
Being a gent, Omarev has explained the entire making of the APK on an Reddit thread. He says that the game is a bit slow when played on the best of Android smartphones so users should bear with him. However, its worth mentioning that Omarev has got everything right with the game other than actually playing it on the itsy bitsy screen. Note that this is actual CS 1.6 running on the mobile OS. If you want to try it out, you’ll need 1.6 in your Steam account for some of the necessary files. For everything else (including instructions), head here.