The I-Team investigated this some time ago, only to be told by ESPN that NFL analyst John Clayton did not have a ponytail but only a "mess of hair in back." Clayton hasn't been seen much in Bristol since then, limiting his exposure to face-frontal shots via satellite, but tonight he made a rare studio appearance in which we see that (at least currently) he does not have the rumored ponytail—but he does have the makings of a mullet, or at least what would be a mullet if he had any more hair.
Case closed!