Some jobs takes two workers to complete. Cutting a piece of 4 foot wide plywood by yourself.....is a real tester of skills. You can hire someone to stand there to help hold the plywood.......or......this is how I do it:
Make your cut 1/4 of the way into the cut line. The plywood should not sagging at this point as seen in the first picture. Apply a hand clamp to both sides of the cut.....as seen in the second picture. The blade wont bunch up now from the plywood. You also have both hands on your saw. Last point to make is....that piece of cut wood wont fall off prematurely and do damage to the remaining of the uncut area.