So umm... What's the go with getting flamed when using Shotguns? Is there something I'm missing?

I decided to use the Judge as KJ in this round where I predicted a rush and got 4 kills within like 3 seconds. I proceeded to get flamed and told to 'kys' by the enemy team. Then my team decided to ask why I'm so cringe? Play properly?

Granted, I'm only 5 months into this game so maybe I need to look up the hidden rules?