when trying to join a server my minecraft crashes

Put the summary of the bug you're having here
when trying to join a server my minecraft crashes
What I expected to happen was...:
Describe what you thought should happen here
What I expected to happen was to join the server and play factions with a few friends
What actually happened was...:
Describe what happened here
Right when the server opened it crashed
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...I opened minecraft
3. ...whent to multiplayer
4. chose a server
5. the server crashed