In my spare time I try to stay active (physically and mentally).
This includes lots of hiking. I recently completed the 48 4,000 ft. peaks in New Hampshire) and am now working through the 53 14,000 ft. peaks in Colorado.
Skiing (all over the Northeast, Tahoe, and of course Colorado). The best is hiking to ski!
I also like to play soccer and volleyball.
And when I have/had more free time I play lots of fantasy sports and moon-light doing football sports analytics. My colleagues Aaron Johnson, Alex Stimpson, and I have written two papers (here and here) for the MIT Sloan Sports Analytics Conference.