Competitive Play is a part of Overwatch's game mode. The play menu is the medium through which the competitive play can be reached. Competitive Play is constructed to be a more serious experience where players compete with each other and are ranked on a seasonal basis. It is currently the only game mode which rewards players with Competitive Points, and a currency to unlock special cosmetic items. Although competitive overwatch is a pretty good system compared to other games with a competitive system, it still has its shortcomings.
The first shortcoming is the problem of the unbalanced matchmaking. If you are not a six-stack, you are not allowed to play a six-stack which is not fair because in other games, a five-man can play a four-man. Also, there is the issue of being rewarded or docked SR based on how the team performs as a whole whereas you are ranked based on your individual performance. So, it's possible that a platinum level player can get stuck in silver because a member of the team can’t play competitive watch. It's quite pathetic.