Sentence:  Hustler ( Knight Dream-Torkin ) <WSD>is</WSD> a playful bay rascal of a colt , not the best gaited , but he surely can pace and is right there with them , and sometimes leading them , in the best miles . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)