OWINGS MILLS, Md. — Big plays — or the lack thereof — have plagued the Ravens in their nightmarish 1-5 start to 2015.The league’s 27th-ranked pass defense allowed three pass plays of 50 or more yards in Sunday’s 25-20 loss to San Francisco, bringing the total surrendered for the season to six. In all, Baltimore has given up 12 pass plays of 30 or more yards despite facing a relatively pedestrian list of quarterbacks through the first six weeks of the regular season.Head coach John Harbaugh and defensive coordinator Dean Pees are beginning to sound like a broken record when discussing the pass defense, but there’s been no apparent improvement as the Ravens are in the midst of the worst start in the 20-year history of the franchise.“If we stop giving up big plays, we’re playing very good defense,” Harbaugh said. “But that’s how it always works when you give up big plays. That’s where all the yards are. That’s how most of the yards are made in this league — by big plays.“It’s hard to methodically go down the field every single series and execute perfectly. There’s no margin for error with that, so you have to be able to make big plays. If you can stop big plays, then you’re going to stop an offense.”After saying only three of Pees’ calls in a total of 90 defensive snaps in last week’s loss to Cleveland were bad decisions, Harbaugh acknowledged a “scheme issue” that resulted in 49ers fullback Bruce Miller’s 52-yard catch late in the first quarter that led to a field goal. The Ravens were in a heavy run defense for a third-and-1 play when Colin Kaepernick connected with a wide-open Miller, a play Harbaugh credited as good scheming on the 49ers’ part.The Baltimore coach said San Francisco’s other long pass plays — the 76-yard touchdown pass to Torrey Smith and the 51-yard completion to Anquan Boldin — were results of poor coverage technique from cornerbacks Shareece Wright and Jimmy Smith, respectively.“I didn’t have any problem with any of the [other] calls yesterday,” Harbaugh said, “but there are always calls that you’re going to look at and you’re going to say, ‘Hey, we could be better.’ You’re going to always try to find things that you could do better. There were no major issues with that yesterday.”Opponents making big plays has been a theme in their five losses, but the Ravens have made very few big plays of their own, failing to recover a fumbled punt or to come away with two potential interceptions against San Francisco on Sunday. Baltimore ranks 30th in the NFL with just four takeaways in 2015 and hasn’t come away with one since the Week 3 loss to Cincinnati.In the 20-year history of the franchise, the Ravens have had six or more takeaways in a single game seven times.Meanwhile, the Ravens offense continued to struggle to push the ball down the field with only one pass play of 30 or more yards on Sunday — the 34-yard touchdown from Joe Flacco to Steve Smith in the third quarter. Through six games, Flacco has completed seven passes of 30 or more yards and only one of 50 or more.“Offensively, we need to start making some big plays,” Harbaugh said. “We need to scheme some big plays in. We need to attack some weaknesses in coverages a little bit better, and we need to make some of those plays. We need to make some catches, need to make some throws, need to make some runs, some run blocks. And we have to do a better job of finding those things for our guys, as well as a coaching staff.”Timeout questionsFacing criticism for the use of two of his second-half timeouts in Sunday’s loss, Harbaugh defended his decisions a day later.After a 17-yard completion to fullback Kyle Juszczyk to open the second half, the Ravens burned a timeout less than a minute into the third quarter because of a play call that was “going to be a disaster” on a first-and-10 at their own 37-yard line with San Francisco leading 16-6.“We wanted to get a good play off there,” said Harbaugh, who did not consider taking a delay-of-game penalty in that situation. “A timeout is not always the most important thing, especially when you’re behind. Sometimes we want to keep drives alive. [When] you start backing yourself up with penalties, I think you’d be asking me that question.”With the 49ers leading 19-13 early in the fourth quarter, Harbaugh elected to challenge the 51-yard completion to Boldin to the Baltimore 25.Despite no visual evidence from camera replays that the play had a chance to be reversed, Harbaugh rolled the dice and ultimately lost his second timeout of the half when referee John Parry ruled the catch to stand. The 49ers scored a touchdown three plays later.“I took a shot there, because it was a big play,” Harbaugh said. “You couldn’t get it on the [stadium video board]. We really didn’t have it on TV [in the booth]. I took a shot there, because it was a big play in the game. We thought we had a chance to win it, and we were hoping we could get it. We had nothing definitive, because we didn’t get much on TV, and we got nothing on the screen.”No update on LewisHarbaugh had no news on starting safety Kendrick Lewis, who injured his left knee in the third quarter of Sunday’s game and didn’t return. Lewis exited the post-game locker room on crutches and was scheduled to undergo a magnetic resonance imaging exam on Monday.“I don’t have any updates on injuries, I apologize,” Harbaugh said. “I have been grinding away on [game] tape. I haven’t had a chance to get to that yet.”James back to HoustonAfter being waived over the weekend to make room on the 53-man roster for running back Terrence Magee, cornerback Charles James was claimed by Houston on Monday.The Ravens signed James to their practice squad in early September after he was waived by the Texans at the end of the preseason. The 5-foot-9 defensive back was promoted to the 53-man roster last week after spending more than a month on the practice squad.