There’s an old cliché in sports that you can’t lose your starting job because of an injury. However, tell that to 49ers quarterback Alex Smith, who completed 70 percent of his passes before suffering a concussion and is currently riding the bench behind rookie Colin Kaepernick.
Smith, the 49ers first-round draft pick and No. 1 overall pick in 2005, struggled in his first three seasons, posting a 57.6 quarterback rating and 4679 yards while throwing 19 touchdowns and 31 interceptions before losing his starting job to J.T. O’Sullivan.  It’s also good to note, however, that Smith wasn’t the only one struggling, as the team had a revolving door at offensive coordinator, forcing Smith to learn a new offensive system every year.
In 2009, Smith replaced Shaun Hill in week 7 against Houston and earned the starting job back; throwing three touchdowns to TE Vernon Davis, causing then-head coach Mike Singletary to name him starter. He entered the 2010 season with the same offensive coordinator for the first time in his career. Smith was booed by the fans at home in week 5 and replaced after injuring his shoulder by Troy Smith.
Jim Harbaugh replaced Singletary and Greg Roman was hired as offensive coordinator in 2011. Harbaugh, an ex-NFL quarterback, felt that Smith would succeed and welcomed him back to the organization.  He put up five comeback victories; four on the road, and the 49ers went 13-3 and defeated the New Orleans Saints in the playoffs 36-32. Smith threw for 299 yards and three touchdowns and also had a 28-yard touchdown run.
Smith was on fire in 2012 before suffering a concussion and being replaced by Kaepernick against the Rams. Kaepernick was impressive in his three games since, leading the 49ers to wins over the Bears and Saints and a tie against St. Louis.
Kaepernick brings a certain element of danger to the 49ers offense with his running ability and strong arm, but Smith is 19-5-1 with Harbaugh and an excellent decision maker.
If the 49ers choose to continue with Kaepernick and leave Smith in limbo, there are teams that could use help at the quarterback position like the Jaguars, Dolphins, and Cardinals, and he could be excellent trade-bait to keep San Francisco an excellent team. But, if they do trade Smith and Kaepernick falters, Harbaugh will have a lot to answer for in the downfall.