You might want to hold the food in a slippery pot right next to the main spot your Cham sits. Make sure the food is alive, Because then he'll know it's food. He'll see the food in the container and probably go after it. If he does eat all around, then try force feeding. If you want more details...
this is chamelias cage. She's about a year old, even though she is not a baby, this is a typical set up for a Chameleon. Make sure when setting up the cage, get Branches close to the light and lots of climbing options. Since they are babies, they will need a much smaller cage (mine is a large)...
Chamelia does it when she gets mad and hisses. But as said in other comments, they randomly do it. Chamelia did it this morning. It's kind of cute though. Lol
Try getting a repti-breeze cage size X-L. My female veiled has a size large of that brand. It is huge compared to her, so I'm sure the X-L will work for your Cham.