Yesterday, the Yankees finalized a deal to ship Randy Johnson to Arizona for a middle reliever and three unimpressive prospects. This is just the sort of trade that drives a know-it-all baseball pundit crazy, because there’s no way to pass smug preemptive judgment on it. Most deals are either clearly good or clearly bad at the time they’re made, and appear that way no matter how they actually work out. If the Yankees trade Kyle Farnsworth, for instance, and he goes and reels off 50 saves a year for five consecutive years, everyone will shrug and say, “Who could have known?” This isn’t that sort of deal. We’ll have to see how Johnson pitches, and how the Yankees replace him, before we can gauge whether or not this was a good call.

There are two ways to look at Randy Johnson. On paper, he was the team’s best starter, and his poor performance last year was largely the product of flukishly bad performance with men on base. In reality, he’s 43 and coming off a year in which he posted a 5.00 ERA. By trading him, the Yankees are implicitly claiming that statistical projections based on his performance in the past few years overrate him, and that the real Johnson is the frustrated old man who tried to pitch the way he had when he was 35 and who had a better fastball any time he got in a jam. This is possibly so, and certainly, few people who were forced to endure watching his miserable, frustrating starts last year would disagree. If Johnson goes out and pitches 200 innings with a 3.50 ERA, though, there are going to be a lot of people saying, “I told you so.” We’ll see how things play out.

I say it’s a good move, for two reasons. The more important is that the Yankees weren’t counting on all that much from Johnson. As long as they can scare up someone to pitch 150 innings with a 5.00 ERA — Phillip Hughes, perhaps the best pitching prospect in baseball, can likely do that while getting acclimated to the majors — their rotation will be fine. Thus, there was little reason not to take advantage of an opportunity to save $10 million and pick up some young players by getting rid of him. $10 million might not seem like a lot, given how rich the Yankees are, but it’s not your money or mine, and it is a lot in any realistic accounting.

The less important reason is that, all else being equal, it’s a good idea for the Yankees to offload a superfluous former All-Star who didn’t really seem part of the team. Picking up random people like Johnson, Alex Rodriguez, Kevin Brown, Gary Sheffield, Carl Pavano, and so on isn’t why the Yankees haven’t won a World Series since 2000, as most players of this class have played wonderfully for them. But on the other hand, Yankee voraciousness has in the past few years been associated with a growing sense of distance between fans and the team, as well as the loss of a sense of team identity. As long as they’re sound on the merits, trades that send these kinds of players elsewhere are to be encouraged.

That leaves the question of what the Yankees got in return. It’s not terrifically exciting, but it’s not bad. Luis Vizcaino is a handy enough pitcher to have around, something like Kyle Farnsworth with more consistency and less upside; he’ll make the bullpen stronger. Prospect analyst John Sickels, whose opinions are worth taking seriously, rated shortstop Alberto Gonzalez and pitchers Steven Jackson and Ross Ohlendorf as the 18th, 19th, and 20th best prospects, respectively, in a deep Arizona farm system. They rate more highly than that in the Yankees’ thin but improving system. All played at Double-A last year; the pitchers are 24, a bit old for that level, while Gonzalez is 23. All of them profile more as fringe major leaguers than as potential stars, but there’s a lot of value in stockpiling ho-hum yet fundamentally sound prospects to increase the odds of having someone in your system make a great leap forward or simply make a useful contribution, thus lessening your need for Jaret Wrighttype players. It’s actually a bit surprising the Yanks got this much considering that Johnson is a dodgy old man (the Yanks are only picking up a few million dollars of his salary). Score one for general manager Brian Cashman.

However this trade works out, it fits into a bigger picture that any Yankees fan must find encouraging. The team is sending off old, expensive players they don’t really need and getting interesting prospects in return. They’re signing free agents to short deals that lessen long-term risk. They’re opening up spots for good, cheap young players. This is what half the know-it-all pundits have been urging them to do for years, this one included. It’s hard to be anything but complimentary when they finally start doing it.

tmarchman@nysun.com