Why is my mesh doing this?

[ethaanw]

Hey everyone, I've been modeling a character for my game and came across this problem with my mesh. I couldn't figure out the problem so even remodelled the whole thing, and its still happening? Does anyone know how I can fix this?

Thanks.

[Ussnorway]

because the weight map is pulling it up with the arms... the fix is to add more vertices to the gut or custom make a new map