Coach Jim Harbaugh, in explaining the move to Smith, could have used the old relationship breakup line: "It's not you. It's me."
2012 Alex Smith Stats
Smith, after all, had seemingly done nothing wrong. He had completed 25 of 27 passes immediately before suffering a concussion against St. Louis in Week 10. Kaepernick played well enough in relief to win the job. Harbaugh said there's no controversy when a team has two good quarterbacks instead of two struggling ones.
But what if Smith hadn't been playing as well lately as that 25-of-27 completion rate would suggest?
Smith had eight touchdown passes with only one interception through Week 5. His Total QBR score was a league-leading 81.1 at that point in the season. The current leader for 2012, Tom Brady, is at 81.6. Smith hasn't played as much in subsequent weeks, but his numbers beginning in Week 6 have dropped off. He has five touchdowns, four interceptions and a 49.8 QBR score that ranks 20th over that span.
Smith was highly effective against Arizona during a 24-3 victory in which he completed 18 of 19 passes. He wasn't as good against the New York Giants or Seattle.
I don't think we can draw concrete conclusions from splitting up Smith's season the way I've done in the chart. But as we look for additional reasons a team would replace a generally successful quarterback, taking a look from another angle cannot hurt.