Giving an entity a /scoreboard score makes you unable to get into a world.

/scoreboard players set @e[r=10,type=Zombie] <objective> 1
This command makes you unable to play on a certain map, when that objectives is shown on the sidebar.

Connection Lost

Internal Exception: io.netty.handler.codec.DecoderException: java.io.IOException: The received string length is longer than maximum allowed (36 > 16)