Ballparking Contest!!!

In case you haven't heard, I HAVE A NEW BOOK!!!!!  To celebrate the publication of Ballparking: Practical Math for Impractical Sports Questions, we're going to have another estimation contest.   

Here's how it works. I’m posting a Fermi question below. To enter, estimate an answer and send it to “aaron at aaronsantos period com.” If your answer is closest to mine, I'll mail you a free signed copy of Ballparking.¹ Second prize receives a signed copy of my other book, How Many Licks? Or How to Estimate Damn Near Anything. Submit your entry on or before June 1, 2012.  Don't worry…I won't spam you or share your email with any third parties.  Here's the question:

When I was a teen, my cousin Nick (who makes a brief appearance in Ballparking) and I used to play home run derby at a baseball field on Sconticut Neck.  Being two years older, I had quite the height/strength advantage and would typically crush him into a metaphorical bloody pulp.  However, once we hit our early 20's, I noticed a striking change.  All of a sudden, the pulp into which I was beating him was dramatically less bloody.  In fact, it was not even much of a pulp:

Me: Why am I sweating?  And what the hell's wrong with the score board?  It says I'm losing!!!"

Here's the field we played on.

Being a teen has a way of disillusioning you into thinking you'll always have a 32-inch waist and be stronger than people that are younger than you.  This is, of course, not the case.   Now that I'm in my 30's my match-ups with Nick have become decidedly one-sided in the opposite direction, and now the vast majority of blood in the pulp is my own.  Fortunately, I still have cognitive dissonance and a healthy dose of wind blowing in from right field.  You see, being on The Neck, the winds tend to blow in off the water.  As a left-handed hitter, I'm at somewhat of a disadvantage to my right-handed cousin.  I've seen (or at least convinced myself that I've seen) some of the tennis balls that I hit go over the fence only to be blown back onto the field.  How fast (in mph) must the wind be to blow a ball back onto the field after it's gone over the fence?

[1] NOTE: I make no pretenses that my answer is correct or even close. Your answer may very well be a better estimate than mine. In fact, your estimate may even be exactly right and you still may not win the contest if somebody else's answer is closer to mine. Sorry about that. This is the best way I could come up with to pick a winner and I'm not changing it now. Like any good game, there's an element of luck required even if you do have great skill. With that disclaimer out of the way, good luck and happy calculatings!