Without looking over your shoulder it’s hard to tell. That said, the most common reasons that come to mind are:
- a dull blade
- trying to make too tight of a turn, too quickly
- trying to cut green or wet wood
- incorrect blade for the cut or material to be cut
- improper tension set on the blade
- trying to cut faster that the wood will allow
When all else fails, read the owner’s manual that came with your saw.