The math is based on runs saved or runs created. Batters faced for pitchers is not necessarily the best measure of impact because as was mentioned more batters/inning is bad. Using innings pitched makes more sense those only counts outs. In 2008 CC pitched 130 innings starting from Brewer team game 90. That means we roughly had (162-90)*9 = 648 defensive innings with CC on the team, and he pitched 20% of them. Each position player only roughly 11% of the PA (obviously more for the 1-2-3 hitters etc). using a very simple approximation, the average ERA in the NL in 2008 was 4.29. An average pitcher with 130 IP would have allowed ~62 earned runs, CC allowed 24. So he saved 38 runs above average. On offense we can use the very simple original runs created formula, RC = TB x (H+BB)/(AB+BB). Yelich in the second half = 182 x (88+25)/(245+25) = 76 runs created total, not above average. That would be .28 RC/PA. In the NL the average RC/PA is .113. So in 273 PA, the league average runs created would be 273*.113= 31. So Yelich has created 76-31 = 45 runs above average. A little more than CC but close.