Looks so much like a warmouth. The main thing is that mouth, kind of small, throws off a warmouth easy ID. Atleast how the picture makes it look.
The spinous dorsal fin "humps" up a bit, doesn't look redear to me. Definatly not a pumpkinseed. Look at the pectoral fin, its short and roundish. Not pumpkinseed, redear, or bluegill like there.
Pumkinseeds, bluegills and warmouth are the sunfish that usually show that rise in the spines of the dorsal fin.
Next the ear, featurless with only a blackish color. The big eye. Big eyes are common on several smaller sunfish, mostly warmouth, bluegills, pumpkinseeds, and redears. But the last three in that list have long pointy pectoral fins. Even young of those species the pecs are showing the length and more pointed than round shape.
Speckly blotchy coloration. Pumpkinseed young, bluegill young, and many other show more of a banded pattern. Warmouth can be banded like when small, but the bands are usually a series of blotches.
Any pictures of this fish not in "action pose"? I suspect how its sitting is distorting what everyone is looking at.
Irate, for once I am not going to say this is a hybrid. It looks like a warmouth to me. Just one with a smaller than normal mouth.
What makes this a warmouth: short pectoral fins, big eye, blotchy color, featurless "ear", no distinguishable fin coloration, mouth in this picture even big, rounded tail. Warmouth are variable, even individuals. A better picture to see its mouth compared to the rest of its features would help. A picture right after it eats a big meal, or better yet during feeding of the meal! In most cases a warmouth will darken up when happy ( or mad). Happy is something going down the gulet.
Even though this a good picture, it is not working really well for ID purposes. I will stick with warmouth until I see a picture that shows the mouth looking even smaller, the pectoral fins pointed, and the dorsal fin spines after the first two looking all about the same length.