Sadly, it appears Ruben Amaro Jr. is going to overpay for Hunter Pence by giving up Domonic Brown and other top prospects. Giving up another a very young, cheap and talented player for a player exiting his prime years, already showing signs of losing power and is expected to make at least $10 million next year and $13 to $15 million the year after that is not good.
It seems many fans assume Pence is a huge enough instant upgrade offensively where the Phillies will be all but assured a World Series. If they truly think that, they don't understand the variance that comes with playoffs.
That brings me to the main point of this article—to see how much better offensively Pence may be over Brown for rest of the season. Certainly, Pence will not continue hitting .309/.356/.472 the rest of the way. His extremely high BABIP will tell you that.
On the opposite end of the spectrum, Domonic Brown will not continue hitting .247/.338/.399 because of a rather low BABIP.
Currently ZiPS projects Domonic Brown hitting .272/.339/.450 for a .343 wOBA in 167 plate appearances. It suspects Domonic Brown's walk and strike out rate will regress but his power will increase.
The latter is much more probable as he still recovers from the power-hindering hamate bone injury he suffered before the season. As for Pence, it projects .286/.335/.474 for a .353 wOBA in 229 plate appearances.
However, I prefer projecting my own way. For both players I'm going to project an even 200 plate appearances the rest of the way. Thus far in the season he's putting the ball in play (AB-HR-SO+SF) in 70.4 percent of his plate appearances.
However, I expect his strikeout rate to drop a small percentage the rest of the season and his home run percentage to be slightly higher, closer to his normal career levels. This would bring his ball in play percentage to 72 percent the rest of the way.
Using batted ball percentages, along with this 72 percent, more in line with his career, his expected batting average of balls in play comes to .321.
Putting those two numbers together brings his non-home run hits to 46. Using his current double and triple rates of balls in play, it brings us to a total of 34 singles, 11 doubles and one triple to go along with seven homers. This also brings us to a .285 average and .468 slugging percentage.
Using the slightly increased walk-rate and change in hits when accounting for BABIP, it brings his on-base percentage to .330. Thus, his triple slash comes to .285/.330/.468 with about four stolen bases.
Projecting for Domonic Brown is naturally going to be more difficult and volatile, given his very small sample size and drastic differences from last year. Like Pence, the first thing to do is regress his walk-rate and strikeout-rates slightly.
In Brown's case, this means slightly less walks and slightly more strikeouts. After regression, I project a total of 23 walks and 36 strikeouts. His more walks will also mean less balls in play per plate appearance than Pence, and subsequently fewer overall hits.
With improving power and some regression, he should hit about six more homers. Using batted ball rates closer to his career norms and a slightly increased strikeout rate, his expected batting average of balls in play going forward comes to .319.
Like what I did with Pence, his expected BABIP along with double and triple rates would lead us to 10 doubles, one triple and 32 singles. This would bring us to a .278 average and .449 slugging percentage. Adding in the walks yields a .360 on-base percentage.
I do not have the exact 2011 weights used for wOBA, but I'd venture to say Brown's line of .278/.360/.449 and similar stolen base total as Pence would come out ahead. Yes, Pence is currently a much better fielder, but offensively there will not be much difference going forward.
Tacking on the age, upside, additional prospects and money, this trade would be a huge mistake.