SANTA CLARA -- Maybe there's a reason why Blaine Gabbert rarely throws third-down passes beyond the first-down marker: Bad things seem to happen.
The 49ers' quarterback hit Vance McDonald for a would-be first-down in the second quarter, but the tight end juggled the throw and it was picked off instead by cornerback Adam Jones.
On San Francisco's next series, receiver Anquan Boldin seemed to pick up a first-down on a third-down toss by Gabbert. But Boldin lost the ball as he was being spun down. The Bengals took over on the 49ers' 11-yard line, and five plays later Jeremy Hill scored a touchdown from one yard out, the first score of the half.
Hill scored again on a one-yard run after a shanked punt by rookie Bradley Pinion traveled only 18 yards and set the Bengals up at San Francisco's 36-yard line.
Finally, another pass to McDonald -- this one on second down -- also was bobbled by the tight end and intercepted by Cincinnati. They converted that into a touchdown on the next play, a 20-yard pass from A.J. McCarron to tight end Tyler Kroft. According to Pro Football Focus, McDonald has dropped five of 27 catchable passes this season, one of the worst rates of any tight end in the lead.
The half ended with the score 21-0 and with less-than-half-full Levis Stadium booing the home team as it jogged into the locker room.
The 49ers entered the game having allowed only 95 points at home (15.8 per game), the best home mark in the NFL. But they’ve also scored the fewest points this season, and they are keeping with that pattern today. They also are 0-7 on third down.
The Bengals turned the ball over in the first quarter when they lost yards on fourth and one. Other than that, the first half was filled with punts -- five by the 49ers, four by the Bengals.
San Francisco shook up its offensive line a bit with starting guard Alex Boone (knee) likely finished for the season. Andrew Tiller moved from right guard to Boone's spot at left guard. Marcus Martin filled in on the right side and Daniel Kilgore started at center.
On defense, Tank Carradine started in place of Aaron Lynch, although Corey Lemonier and Eli Harold also have filled in throughout the first half.
Running back Shaun Draughn suffered a knee injury in the second quarter and did not return to the game. Travaris Cadet has taken all of the snaps at running back since then. Kendall Gaskins is the only other running back active for this game. Jarryd Hayne remains on the practice squad.