2009: 28th in passer rating, 18th in yards per attempt, 29th in completion percentage (out of 32 qualified quarterbacks)
2010: 27th in passer rating, 26th in yards per attempt, 29th in completion percentage (out of 31 qualified quarterbacks)
2011: 23rd in passer rating, 27th in yards per attempt, 28th in completion percentage (out of 34 qualified quarterbacks)
2012: 29th in passer rating, 26th in yards per attempt, 31st in completion percentage (out of 33 qualified quarterbacks)
In recent memory, the only other quarterback this bad through his first four years given this much rope is Alex Smith, but Smith had far fewer pass attempts. In his first four seasons, Sanchez has had 1764 attempts (with five games left), while Smith only had 1172.