The intersection of a few factors usually combine to make a fine player underrated, or largely unnoticed in comparison to his abilities and accomplishments.
Often a very good player toils in relative anonymity in a small market, or on non-winning teams. More often, as in the case of ex-Celtic forward Cedric Maxwell, the underrated star plays on strong clubs surrounded by greater or more celebrated teammates.
Jamaal Wilkes fits this bill well, having been overshadowed at UCLA by Bill Walton, at Golden Stae by Rick Barry and later with the Lakers by Kareem Abdul-Jabbar and Earvin Johnson.