How old is he? How many hens/roosters are in the same area?
I might guess that the other roosters might be picking on him. Next time he is out, see how he reacts with the others. You may need more hens or to separate him out with a few of the hens.
You have too many cockrels for the size of your flock, and space available. Either more birds, separate digs, or eliminate one or two of the boys. Mary