KANSAS CITY, Mo. (AP) – There may be no more important piece to the Kansas City Chiefs’ puzzle this season than quarterback Matt Cassel.  After paying his dues at USC and with the New England Patriots, Cassel was given a chance to shine when he was traded to the Chiefs. His first season was one of progress, but his tremendous growth last year was a big reason the Chiefs went 10-6 and won the AFC West.  Coach Todd Haley understands that the team’s fortunes again rest on Cassel’s right arm.  Haley said the biggest thing that Cassel needs to do is understand his own players, and the match-ups they create. That has been difficult with wide receivers Jonathan Baldwin and Steve Breaston missing time because of injuries.