1 - Make sure you have Counter Strike installed
2 - Download YAPB http://forums.bots-united.com/showthread.php?t=9986
3 - Extract the zip and move the folder addons with all the content to ~/Library/Application Support/Steam/steamapps/common/Half-Life/cstrike
4 - After that, open the file liblist.gam in the folder above and replace gamedll_osx "dlls/cs.dylib" with this content:
//gamedll_osx "dlls/cs.dylib"