UPDATED 8/30 First I thought it was a young male, just getting his feathers. Then, looking more closely, I thought it was a female who had been in a fight, based on a long streak of red on the belly. Bisbee Border Bird Bloggers (say that five times fast!) however, believes it is a molting male, and that the red streak is the skin showing beneath a featherless area on the belly.
(You can't see it too well in this photo.)
After reading Bisbee's comments, I'm inclined to go back to my initial thought that it is actually a young male, since I have 2 other young males who are just getting their red feathers this week. Not nearly as visceral and dramatic, but cool, nonetheless! Thanks for the info, Tom & Sheri!