Our male lead spends 3 weeks lost alone in a pretty tame looking forest, having been washed up on a beach somewhere with a mate, who he resuscitates (nice use of black and white to convey that flashback moment). 30 seconds in my partner turned to me and said "Bet you he's eating ..." (yes, that's right - unfortunately the plot direction was a very transparent in that regard). The tennis ball was a bit disconnected from the storyline. It wasn't enough Horror or Splatter for me - pretending to eat a bit of raw meat wasn't quite enough to sell me on the genre aspect. The title cards were a bit over-used and the sound was all over the place.
I think you had a reasonable idea but it might have worked better in reverse, so starting at the end. Like: retold by the survivor to those at the camp site, later at night around a fire, until we get to the end of the flashback story and only then discover the source of the food supply. And it needed blood, lots of blood ... there was none. (Golden syrup, red food dye and a bit of water is wonderful for making this).
This one was about a man lost in the forest, eating a lot of mysterious meat which leads to *spoilers!*. Plot was predictable and soundtrack was a little over the top at times, but with a bit of cleaning up it could be pretty creepy.