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SANTA CLARA -- Cornerback Tramaine Brock, who sustained an ankle sprain early in training camp, provided the highlights Wednesday in a 49ers practice that coach Jim Harbaugh cut short at Levi's Stadium due to poor field conditions.
Before moving to the solid footing -- and privacy -- of the 49ers' practice fields behind the team's training complex, Brock demonstrated why the 49ers are counting on him to be the team's top cover man.
Brock broke up a Colin Kaepernick pass intended for wide receiver Quinton Patton. Then, a short time later, Brock jumped David Reed's route at the right sideline to intercept McLeod Bethel-Thompson for what would have been a pick-six interception.
Brock is set to open the season as a starter for the first time in his career. Last season, he replaced veteran Nnamdi Asomugha as the team's third cornerback early in the season. Then, he moved into the starting lineup when Tarell Brown sustained a ribs injury.
Brock started the final seven regular-season games of the season and led the 49ers with five interceptions.
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The practice session was the last time that up to 10,000 fans were allowed to watch the team practice. But less than one hour into a scheduled 2-hour, 15-minute practice, the 49ers left the field due to unsafe turf.
In other notes. . .
--Backup quarterback Blaine Gabbert completed each of his six pass attempts during 11-on-11 drills. All of his passes were short tosses.
--During a 7-on-7 drill, Josh Johnson found Lance Lewis on a short touchdown pass against the coverage of linebacker Michael Wilhoite and safety Eric Reid.
--Colin Kaepernick and veteran wide receiver Stevie Johnson could not connect on a couple of back-shoulder pass attempts, including the first throw of 11-on-11 drills against Chris Culliver's coverage.