After last night, BJ Upton is sporting a healthy .294/.359/.794 postseason line. The batting average and on-base ability are in line with his established performance level, but that slugging is just off the charts. Looks like the shoulder that was bothering him all season might be back in working order.
It brings to mind the question: should his hot postseason hitting change our expectation of him going into next year? It’s only 40 PA, but he’s already hit half as many homers in the last eight games as he did in the entire regular season.
Using his regular season stats and running a Marcel projection, Upton figures to hit something like .285/.380/.437 next year. That’s pretty darn good for a young centerfielder, and with acceptable defense it would make him one of the best under-25 players in baseball.
If we throw in his postseason stats, that projection jumps to .284/.380/.447. That difference is mostly a projected increase in his – you guessed it – home run rate, from 16 per 650 PA to 18 per 650 PA. Not a huge difference, but there it is.
The analytical community doesn’t normally include postseason stats when making projections, and I’m not sure why (beyond the practical reasons that the data sources keep the two seasons separate). It seems weird to use less data rather than more, and the postseason is just as much part of the performance record as the regular season. So, yes, Upton’s power-hitting in the postseason does slightly change our perception of him as a batter, but not by a lot.