Billy Wagner is 38 years old and recovering from major elbow surgery, and tonight he will join a Red Sox team in the heart of an intense playoff race. The Red Sox believe Wagner can help them, a determination they were forced to make quickly and one requiring far more than a simple trip to New York.

In many ways, the scouting of Billy Wagner has been going on for years.

"Actually, I had my wife get an old report because I saw him in college," said Allard Baird, a special assistant to Red Sox general manager Theo Epstein who was among a group of club officials involved on the decision to acquire the veteran lefthander. "I saw him in the minor leagues and I saw him in the big leagues, too. I saw him last year before the injury.

"In this particular situation, you look for differences," Baird said. "That’s not being negative, but you go in looking for differences and hoping you see consistencies."

So this is how it worked on Wagner, from Baird to Epstein to Galen Carr, Ray Fagnant and Jamie Bane, all (and more) of whom were involved in an aggressive and risky roll of the dice to add a power lefty to the Boston bullpen. Carr and Fagnant were in New York when Wagner made his return to the majors last Thursday.

And in evaluating whether Wagner was worth a gamble requiring the Sox to part with $3.5 million for six weeks of service -- the players who will be dealt to New York are a far lesser and relatively inconsequential price -- the Sox relied on a scouting history that began roughly 15 years ago, when Wagner was firing bullets for Ferrum College.

For Baird, formerly the general manager of the Kansas City Royals, scouting Wagner was not merely as simple as looking at radar gun readings and assessing the sharpness of Wagner’s slider. He collected information on Wagner’s pregame routine and watched him stretch. He paid attention to Wagner’s warmup sessions, taking particular note of how long it took him to get loose, how he stretched, what pitches he focused on. He compared all of that information to his own personal reports and those compiled by Red Sox scouts over the years, all in an attempt to answer a few simple questions.

How close is Wagner to being the same man who has amassed 385 career saves? Are his fastball and slider still good enough to be effective at something less than 100 percent? How is Wagner’s psyche in the wake of elbow surgery, specifically as it pertains to his aggressiveness and intensity?

And ultimately: Can he help?

"You look at past video before he had the surgery, you look at past reports, you look at all those things before you even see the player perform," Baird said. "A lot of those things are subjective, but they can be useful. …Theo is an extremely detailed guy. We took the approach where we had people in the office looking at video, scouts in the field, everything.

"The thing is, he is coming back from rehab, but the arm strength is there and the aggressive with that arm strength is there. That’s a big factor, too. There’s no reluctance to be aggressive in the strike zone. The last outing [on Monday], you could tell watching him warm up that he was antsy to get in the game."

Whether all of this will pay dividends for the Red Sox is anybody’s guess, though it should be stressed that the cost here for the Sox seems relatively small. After all, it’s only money. The Red Sox have a deep bullpen. Their success or failure does not hinge on Wagner’s health nearly as much as it does on several other factors, from the depth of their starting rotation to the consistency of their lineup. For the Sox, Wagner is a luxury.

So why did the Sox make this move? Because even with 5 mph shaved from his fastball, Wagner still throws harder than the large majority of lefthanded relievers in the major leagues. Because he gives the Red Sox another potential weapon. Because the Red Sox are a big market team that can spend $3.5 million on a player for six weeks of service and be none the worse for wear, and because the Sox came away convinced that Wagner still has enough juice -- even after Tommy John surgery -- to be far more effective than most big league relievers.

Even so, rest assured that this was an unusual acquisition for any major league team, even one with a big payroll and more than its share of issues. As the Red Sox learned with John Smoltz, players rehabilitating from injury are a great risk, even if the potential reward is high. Wagner’s elbow could flare up at any time and the Red Sox could be out another $3.5 million. But as Billy Wagner joins the Red Sox tonight at Fenway Park, know that the Red Sox have been watching him a long time on the odd chance that he might someday be able to help them win a world title.

Now you know why your parents always urged you to do your homework.