SANTA CLARA -- How fast can the 49ers defense adjust to Trent Richardson's sudden arrival in the Indianapolis Colts backfield? They'll find out Sunday.
In a stunning trade Wednesday, the Colts acquired Richardson from the Cleveland Browns for a 2014 first-round draft pick. Richardson was the No. 3 overall pick in last year's draft, selected two spots after the Colts took Stanford quarterback Andrew Luck.
Wednesday's trade went down while the 49ers were finishing practice. Defensive coordinator Vic Fangio is scheduled to speak to the media Thursday.
Earlier Wednesday, linebacker NaVorro Bowman explained how Luck thoroughly dominated the 49ers' film study of the Colts offense.
"It's really just No. 12, man," Bowman said. "I feel like they feed off of him, and he runs pretty much every phase. We know that he likes to get our looks early before the ball is snapped. So we're going to have to do a good job holding our coverages and holding our disguises."
Luck figured to be handicapped to some extent, having lost three offensive cohorts to injuries in the past week: running back Vick Ballard (knee), tight end Dwayne Allen (hip) and guard Donald Thomas (quadriceps).
The Colts' backfield still has a longtime 49ers nemesis in Ahmad Bradshaw, the former Giants tailback.
Richardson, an Alabama product, offers a different look. As a Browns rookie, he proved he can run well (950 yards, 11 touchdowns) and also catch (51 receptions, 367 yards, one touchdown).
The 49ers run defense likely isn't shivering at Wednesday's late addition to their Colts' scouting report.
For one, the 49ers perennially have proved adept at stopping the run, although Seattle's Marshawn Lynch ran for 98 yards and two touchdowns in Sunday's 29-3 rout of the 49ers.
More pertinent, the 49ers' focus likely remains on Luck, whose top targets this season have been veteran Reggie Wayne, second-year standout T.Y. Hilton, former Stanford tight end Coby Fleener and ex-Raiders wideout Darrius Heyward-Bey.
So how do the 49ers fool Luck?
"The answer isn't a real good one, because there's not a lot that confuses him or rattles him," coach Jim Harbaugh responded about his former pupil. "There's very little that he doesn't handle well."
After helping Harbaugh usher Stanford's program into national prominence, Luck took the Colts to the playoffs last season as a rookie starter. He set NFL rookie passing records for yards, attempts and 300-yard games.
Luck said "it'll be sort of fun, I guess" when he reunites Sunday with Harbaugh and other former Stanford coaches, such as coordinators Greg Roman (offense) and Fangio.
"I definitely feel he helped me get to where I am," Luck said of Harbaugh on a media conference call Wednesday morning. "He obviously helped turn Stanford around, his efforts more than anybody. Some of my success was being able to play at a well-coached, well-run program."
Harbaugh appreciated those "very generous" words and returned the flattery, saying how Stanford "drew the long straw" with Luck's presence as more than a "freakishly good athlete."
Luck's intelligence is a trait Colin Kaepernick first recognized in 2010 when they attended the Manning Passing Academy. Said Kaepernick: "He's a great quarterback, very intelligent, very intuitive, knows what he's doing on the field."
Now everybody waits to see what Richardson will be doing on Candlestick's field Sunday.
Former Colts president Bill Polian thinks Richardson can easily contribute against the 49ers, aside from pass protection in blitz situations.
"Nomenclature would not be a problem because Andrew's smart enough," Polian said on SiriusXM NFL Radio. "(Luck) knows everybody's assignment on every play, so he could tell him what to do."
Indianapolis (1-1) at 49ers (1-1), 1:25 p.m. CBS