KANSAS CITY, Mo. -- A snowstorm is churning its way toward the Plains, but since Thurston Smith has you here, he'd really like to show this little DVD he put together.

It's not long, he promises as he fumbles through some discs. He made it before his son left home in 2011 to play in the NFL. It's touching and cheesy, filled with prom pictures, Bible verses and slow-thumping R&B music. It's something a parent puts together when he knows his son's life is about to change. Predictably, Aldon Smith, a big, bad linebacker who is paid to terrorize quarterbacks, thought the compilation was a bit much. But someday, Thurston knows, his son will appreciate it.

Life is happening fast for the kid right now. A month ago, Aldon Smith was considered a candidate for defensive player of the year and was zeroing in on Michael Strahan's 11-year-old single-season sack record. He was so hot that in a promo for the "Sunday Night Football" game between his San Francisco 49ers and the New England Patriots on Dec. 16, his face was featured prominently next to Tom Brady's. Smith got a kick out of that.

Four weeks later, he's mired in what many in the Bay Area are calling a slump. He didn't have a sack in that game, or the last two of the regular season, and was recently criticized in one of the local newspapers for appearing disinterested. He's considered one of the biggest question marks as the 49ers begin their quest for the Super Bowl on Saturday in a playoff game against Green Bay.

Thurston Smith doesn't worry too much about it. This, he says, isn't really stress.

Stress is the phone ringing in your North Kansas City home six and half months ago, on a summer weekend, when you're getting ready for church, and a reporter on the other end asks if your kid is OK. Stress is hearing that there had been a stabbing the night before, at your son's house 1,700 miles away, and then having a whole bunch of other reporters with California area codes call.

Thurston had to tell them all "no comment," because he couldn't tell them that he had no clue what was going on because he hadn't heard from his kid. This is where Aldon Smith was 6½ months ago. This is how fast his life has moved.

On June 30, at a party he was hosting, Aldon Smith was stabbed twice trying to break up a fight. One of the wounds was centimeters from his heart, but he was OK because he's healthy, muscular and lucky.

Then again, he wasn't OK. The incident, coupled with a DUI days after the 49ers' season ended in the NFC championship last year, raised serious questions about where the second-year linebacker was headed.

Was Smith, a Midwesterner who played the drums in his church choir, becoming an NFL cautionary tale? Could he stay out of trouble? Could he be counted on?

"I worry more in the offseason," Thurston said, "because he's not in a structured environment. I worry about him from the time that last game of the season is over with. He has nothing but time and money on his hands. I know what he's like when he's not structured. He's all over the place. He's young and full of energy.

"If he could play football 12 months out of the year ... I wouldn't have to worry about him at all. Because he's doing something he loves. I think he's doing something that God has blessed him with."

Pursuing a goal

The opponents don't know this, that Aldon Smith is boiling inside, and anything can happen. Smith is at his best when people expect the least. If there's one thing he hates, that motivates him more than anything else, it's when people doubt him.

After last summer's troubles, Smith set several preseason goals: He wanted to hold up his end as a starter, wanted to be the consummate teammate, and he wanted to get 23 sacks. The last one was a seemingly outrageous goal; the NFL single-season record was 22½. Smith claims he had no idea of this, and simply picked it because he was turning 23 in September. On his birthday, he told his dad that 22 was a tough year, but 23 was going to be better.

Playing with a broken bone in his leg, Aldon Smith helped lead the Missouri Tigers to an upset win against Oklahoma. Dilip Vishwanat/Getty Images

The 2012 NFL season will be remembered for individual greatness, for Adrian Peterson's gallant run toward history, Calvin Johnson's record-breaking catches, and for a wild November when it looked as if three young defensive stars -- all second-year players -- would shatter Strahan's sack mark.

Smith seemed primed to get there first. He had 19½ sacks by early December, while Houston's J.J. Watt and Denver's Von Miller hovered close behind. Smith donated $5,099 to the local Boys and Girls Clubs for each sack, and the amount got so big it accounted for roughly one-tenth of his salary.

Quietly, over the span of a few months, he evolved into one of the most disruptive forces in the NFL. He broke Reggie White's record as the fastest player to 30 career sacks (Smith did it in 27 games; White did it in 28), and eclipsed the single-season franchise mark of 17.5 by Fred Dean that had stood for nearly three decades. But he was no longer anonymous on Nov. 19, when he had 5½ sacks in a victory over the Chicago Bears on "Monday Night Football." Smith texted his friend Miller that night after the game. The count to history was on.

But none of the young pass-rushers made it to 23, and Smith's hopes all but ended on a cold and rainy Sunday night in New England on Dec. 16, when his teammate, Justin Smith, went down with a triceps injury.