SANTA CLARA, Calif. (AP) Eric Reid got a quick lesson on the Black Hole, a new term for the second-year San Francisco safety.
''I don't even know what the Black Hole is, what is that?'' Reid asked, standing at his locker Wednesday at the midway point of preparations for Sunday's game at Oakland.
Ah, yes, those crazy characters all dressed up in the Coliseum end zone.
Doctors. Lawyers. Techies. School teachers.
''I've seen highlights on TV. They get pretty dressed up, right? That'll be fun. I like that kind of stuff,'' Reid said. ''My dad is a pastor and he likes to get dressed up in motorcycle gear and try to act tough. It's good to change it up a bit. I bet they enjoy it.''
Reid and the 49ers' defense have been doing their part to carry the load in recent weeks, and now San Francisco (7-5) is playing for its playoff life as it makes the short road trip to Oakland (1-11) on Sunday, likely needing to win its four remaining games or at least get some help.
''We could play better. There are some plays that cost us games in the earlier part of the season,'' Reid said. ''We dug ourselves into this hole and we've got to climb out of it.''
On a defense that has been defined by its moving parts and injuries as much as its playmaking ability, it has been a tough year to establish the momentum of recent seasons. Linebacker NaVorro Bowman continues to rehab his surgically repaired left knee that has kept him out since the injury in January's NFC title game at Seattle, and the 21-day window for him to be activated will end Monday.
Linebacker Patrick Willis was lost for the season because of a troublesome left big toe that required surgery, while Aldon Smith spent the first nine games serving a suspension by the league. Nose tackles Glenn Dorsey and Ian Williams have dealt with injuries, too, with Williams going on season-ending injured reserve for the second straight year.
Michael Wilhoite and Dan Skuta have emerged as reliable linebacker replacements, and rookies Chris Borland and Aaron Lynch have become key contributors out of necessity at the position.
''Just as a defense we're not going to fold in, we're not going to fold our tents up just based on what's happened,'' captain Justin Smith said Wednesday. ''Guys have responded. Young guys have played well. Hats off to those guys, they've kept the level up there.''
The 35-year-old Smith's body feels better at this stage of the season given he has regularly taken off Wednesday practices to rest his body, something the coaching staff supports as an approach to ensure Smith is at his best on game days. He has 36 tackles, five sacks and two forced fumbles this season.
Smith underwent surgery for a partially torn left triceps following the 2012 Super Bowl season, then dealt with a nagging shoulder issue much of last year.
He hasn't decided whether he will return for a 15th NFL season next year.
''I haven't given it any thought,'' Smith said. ''It will be something to think about after the season.''
He has more pressing matters, such as chasing down rookie Raiders quarterback Derek Carr on Sunday. Smith and the 49ers realize Oakland will be looking to restore some respectability on the heels of a 52-0 loss at St. Louis.
Two key members of San Francisco's 2013 secondary are now with the Raiders - cornerbacks Tarell Brown and Carlos Rogers.
Smith praised the new secondary featuring safety Antoine Bethea and said what makes it work with new faces is keeping things simple and basic execution.
''It's a credit to these guys coming in, stepping up and making it important to them. That's the biggest thing,'' Smith said. ''The level's been raised here on how we play defense. These guys came in and they didn't want to see that bar go down, and it hasn't.''
When it comes to the offensive struggles, Smith says, ''I stay on my side, I stay with what I know.''
''We're just going to rely on our offense to come around,'' Reid said. ''We need them to win these games, they need us. We've just got to count on each other.''
NOTES: LT Joe Staley didn't participate in a practice that was moved up several hours to late morning because of steady rain. Coach Jim Harbaugh said he was throwing up. ... RT Anthony Davis, who has missed the last two games nursing a concussion, was set to do some cardio work and weightlifting.
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