Scouts use a 20-80 scale to place grades on tools for prospects, where 50 is generally considered “MLB average,” 60 is above average (sometimes referred to as “plus”) and 70 is well above average (or plus-plus). The elusive 80 grade refers to an elite tool, or one of the top 1 percent in the game. Think Stephen Strasburg’s fastball or Ichiro’s ability to hit for average. But the “power” tool is a little harder to get a feel for.
Plenty of prospects carry plus raw power but never make enough contact at the higher levels to manifest it. Scouts often look at bat speed and leverage to determine just how much pop a player has in his bat. Since we’re talking purely raw power, that’s not a bad way to look at the tool. However, power, in terms of isolated power (the delta between a hitter’s slugging and batting averages), can be manifested in more ways than just tape-measure home runs. I think it’s helpful for the more statistically oriented fan to get a feel for what a power grade may translate to at the big league level. Keep in mind that grades are future projections, and most prospects fall short of future projections.
In the past I’ve used the following as a back-of-the-napkin translation from power grades to ISO-P:
30 – .80-.110 (Well below average)
40 – .120-.140 (Below average)
50 – .150-.170 (Average)
60 – .180-.200 (Above average)
70 – .210-250 (Elite)
80 – .280+ (Bonds; Pujols, Ruth)
Note that scouts often assign mid-grades like 55 (which explains the gaps between ranges).
What we’ve seen in the last season-and-a-half, however, is a relatively sharp cliff in power production. The average AL ISO-P from 2003-2009 was just over .158, with no single season average below .152 and none higher than .163. In 2010, however, the AL ISO-P fell to .147. Through a little more than half the season in 2011 the AL ISO-P is .144.
I don’t mean to suggest that power numbers will continue to be suppressed, as 1-2 season dips are not uncommon, but I should adjust the numbers slightly to translate to today’s AL offensive environment. I’d say knocking off .oo5 to .007 points of ISO-P is a fair tweak.
Remember, these are just ballpark numbers and that one must make solid contact enough to manifest both raw power and ISO-P. But for those who gravitate to numbers over scouting reports, I think this scale is a fair translation of projected future production.







