I reported a player who used this glitch, but in skywars you can do /Shop : With the : and go into the shop, same with /kit skyknight : I can show the player who used this glitch in the screenshots below

 

Yes, this is a well known glitch and people do abuse it. It is bannable, so if you see people using /shop in the lobby, please feel free to report them for it. Going to close this since its been a glitch as long as I can remember. Thank you for reporting it.