Lots of good suggestions from members - all of them work!!

Bring the bobbin thread to the top as in quilting and begin slowly. Does it happen. Could also use apig.

Is the bobbin wound properly? Sometimes a wonky wind results in a mess. Is the bobbin seated correctly? Is the machine threaded correctly? Is the needle dull? I have generally found the reason by going through the "start the threading process from scratch" - good luck.