When John Hester came to the plate as a pinch-hitter last month - and promptly homered - he became the ninth player to make his major-league debut this season in an Arizona Diamondbacks shirt. It seems like we'd seen that happen quite a lot this year. But how does the number of rookies, and the playing-time they have received, stack up against previous Arizona seasons? Does this indicate 2009 was a 'rebuilding year' - a notion rejected by Derrick Hall in a recent chat - or is just the normal turnover resulting from injury and other issues?

Firstly, let's just take a look at the players who made their major-league debuts with the Diamondbacks. I've divided these into two categories: those called up during the bulk of the season, and September call-ups, as the latter likely deserve separate consideration. [* = 2009 wins total is extrapolated to 162 games]

It's probably no great shock to see that 2004 had the highest number of AZ debutants and 1998 the next most - indeed, the opening game in franchise history alone, was the first appearance of three players, Travis Lee, Scott Brow and Edwin Diaz. Generally, it seems true that the more rookies that you need to use, the fewer games you end up winning. This probably makes sense; mid-season call-ups are needed to replace those who are injured or ineffective, and they will be, almost by definition, replacement-level players.

Given this,  a couple of aberrations stand out. Our World Series team in 2001 saw a record number of September call-ups, though the players concerned contributed zero at-bats or innings to our post-season performance. Indeed, only one of the eleven newcomers all year saw any playoff action: Troy Brohawn ended Game 6 in the World Series, when we were 15-2 ahead. 2003 is also interesting: we'd used ten rookies by the All-Star break, but still had a winning record. However, their quality was generally more than replacement level, especially pitchers Brandon Webb (a 2.84 ERA in 180.2 IP), Oscar Villarreal (2.57 ERA, 98 IP) and Jose Valverde (2.15 ERA, 50.1 IP).

However, not all debutants are created equal. Their impact ranges from the 562 at-bats by Travis Lee in 1998, all the way down to the one (and a strikeout, at that) from Ken Huckaby in 2001 - hey, at least he can stil say he played for a World Series-winning team. I wonder if he got a ring? So, let's narrow it down with an (admittedly arbitrary) standard of what constitutes an 'impact rookie' - 100 plate-appearances or thirty innings pitched. How does the numbers stack up then?

That's an average of 3.3 impact rookies per year. Given this, the degree to which the team relied on its young players in 2003 and 2004 becomes very apparent from the chart above, with as many or more 'impact rookies' in each season as from 1998-2002 combined. As noted above, one can only wonder how awful our 2003 record might have been, had we not got 329 innings at an ERA+ around 175 from Brandon Webb et al. I also note that very few of the relatively large raw number of 2001 rookies qualified as having an impact.

If we've been rebuilding of late, there hasn't been quite the same influx of newcomers to the big leagues in the past couple of seasons. While we're not done yet this year, with only 18 games left, Brandon Allen has about the only chance of joining the list for 2009, with 67 PAs before today. While Trent Oeltjen has a few more, his playing-time has all but evaporated with the return of Chris Young and Eric Byrnes. Bryan Augenstein (15 IP), could possibly also get there, especially if he ends up replacing Max Scherzer down the stretch.

As a final measure, we can add up the number of PAs and IP by debutants, to give an overall measure who reliant the team was on newcomers. For this measure, I'm allowing September call-ups to count both in their first season and the one which followed, since the September playing-time is often more a token gesture than anything. It'd be nice if baseball-reference.com allowed you to restrict results to rookies in its Play Index. Would certainly have made compiling this chart a good deal easier. Note that if a player was a Sep. call-up on another team, his second year stats in AZ aren't counted. I can't think of many such cases, though I have included Kevin Mulvey, who debuted for the Twins earlier this year, before being traded to Arizona. PA's by pitchers aren't included.

The last column, 'Rookie Factor', is a measure which combines the two numbers, innings pitched and plate-appearances. In 2008, the average inning lasted 4.32 PAs, so I multiply the rookie innings pitched by 4.32, and add the number of rookie PAs. This gives a number approximating the total number of Diamondback PAs, for which our debutants were responsible during the season, on both sides of the ball.

Again, this shows how vital the farm system was to the Diamondbacks in 2003 and 2004 - in the former year almost 35% of the innings pitched were by players in their first major-league season, more than twice as many as in any other year. Similarly, 24% of the at-bats in 2004 were from new players, a figure six hundred above the highest other mark, even allowing for what's left in 2009. This isn't necessarily a bad thing: it depends on the quality of the players, and any team will always have injuries in the course of the season - these holes needed to be filled, whether with veterans or not.

As a measure of rebuilding, it seems that this season, while it has had its moments, falls short of what the team went through in 2003-04, and looks to end about the middle of the pack, in franchise history. If I had to predict for next year, I think/hope that we will have a fairly-stable core of players, at least as far as the starting roster goes. There are certainly questions over a number of positions, but in most cases, it appears to be more a question of choosing between a number of (more or less qualified) candidates for the spot, rather than having an absolute questionmark.