Early in the third quarter Sunday, Frank Gore took a handoff through the middle of the Cardinals defense, picked up terrific blocks by guard Mike Iupati and receiver Michael Crabtree and scooted into the end zone for a 37-yard touchdown.
The 49ers led 19-7 and appeared to be in excellent position to do what the offense does best: Grind away at both the defense and the game clock with its big offensive line and effective running game.
It didn't happen that way. Gore carried the ball only two more times the rest of the game and wasn't on the field for the team's final two snaps. On Monday, coach Jim Harbaugh explained why. "He's got some things," Harbaugh finally said after prodding. "He's not 100 percent. We have other backs that got carries in the second half."
Harbaugh did not divulge exactly what is bothering Gore, the team's workhorse running back since 2006, and Gore was not on the 49ers' injury report in the week leading up to the Cardinals game. Gore has dealt with sprains to both ankles this season - they occurred in Week 3 and Week 9 - and he suffered a sprained knee early in a Week 10 win against the Giants.
That injury coincided with a notable dip in his production.
Before that game, Gore had rushed for 100 or more yards in five straight contests. He left the game against the Giants with six carries for zero yards and hasn't reached the 100-yard barrier since. His only touchdown in the last five games came Sunday.
The injury also appears to have influenced the 49ers' offensive game plans. Before the Week 10 game against the Giants, the 49ers had been a run-heavy team. Prior to that game, they attempted 246 runs against 228 passes. In the five games since, that ratio has flipped. The 49ers have run the ball 145 times and called 174 pass plays.
Sunday's game in Arizona was the most lopsided ratio of the season. Counting the times that Alex Smith was sacked - five times - the 49ers attempted 42 passes against only 21 carries. After Gore's touchdown at the 12:24 mark in the third quarter, the 49ers ran the ball four more times - two by Gore and two by backup Kendall Hunter.
Gore and Hunter appeared to alternate carries. Gore gained eight yards on the first play of the game, and then headed to the 49ers bench while Hunter entered the game on second down. Hunter also was on the field for San Francisco's final two offensive snaps. The 49ers needed a yard for a first down and the 49ers tried unsuccessfully to throw for it on both third and fourth down. Smith's last attempt went through the hands of a diving Hunter.
Gore and his teammates will get an extra day to rest this week. They host the Steelers on Monday, and they won't begin practicing for that game until Thursday.
-- Matt Barrows