First off, let’s take a look at the applicable definitions of the word chemsitry, from dictionary.com:
sympathetic understanding; rapport. the interaction of one personality with another
Rapport. Rapport is an interesting word when talking about a quarterback and his wide receivers.
Mark Sanchez has not kept a group of wide receivers together from year to year. The only one that has been with him his entire career is Dustin Keller. Through the years, favorite targets of his have come and gone, such as Braylon Edwards and Jerricho Cotchery. As such, the issue of chemistry is one that is revisited from year to year, which makes it even more important.
Why is it so important?
Look at the great offenses around this sport through the years. Look at Peyton Manning and his Colts crew through the years. How about Aaron Rodgers and his core? Even (sigh), Tom Brady and his 8 million weapons. For the older fans, think about the vintage San Francisco 49ers teams with Bill Walsh.
What do they have in common?
The quarterback, in all cases, is in perfect sync with the wide receivers. When you drop back to pass in the NFL, you have at most, 3 seconds to get rid of the football. The quarterback must know where his receiver is going to be, before the receiver gets there in order to be successful. On the great teams, the ball is released as the receiver is making his cut. The catch is made in stride, for the most yards after the catch possible.
What does that take? Timing. How do you perfect timing? Establish chemistry with the wide receivers.