Thanks for the inquiry!

Most likely it's a gear problem...I'm not terribly up to date on my technical knowledge of the Ridgid recip saws but I would say that one of the main gears or wobble gear inside the gear case is either chewed up or worn down so badly that with any pressure or stress, the gears slip and the unit won't run. I would probably have it diagnosed at a repair shop or you can take apart the saw and take a look at the gears to see if you see anything obvious.

If you'd like more technical assistance you can also contact Ridgid's tech line at 888-743-4333 or 800-521-6535.

I've attached a parts breakdown to this reply for your reference, it's for an R3002 model which is a 9amp saw although I'm not sure what your model# is so it may not be 100% identical.
I would make sure the Thrust Roll Bearing and the Gear Linkage Assy look like they're in good shape, to start. If you do find the answer to this problem PLEASE feel free to post it hear for others, we'd appreciate it.
Thanks again!
- MTR