Imagine This. . .

You're a 5'4" 160lb dude in his late 30s playing a friendly game of softball in a community league.

*THWACK*

From right field, you see the ball fly up in the air heading towards that gray area between right field and center field.  You've got tunnel vision, and all you can see is that softball floating through the air as you sprint, full speed, in order to make the play.

Unfortunately, for you, the 6'4" 250lb center fielder also has tunnel vision for that softball and is sprinting toward the same spot.

*BAM*

An unholy crunch echoes through the field as the two of you collide, the larger dude basically running right over you.  With his height, your *ahem* lack of height, and the two of you both sprinting, this lines up two horrible, horrible body parts that one never wishes to have lined up in this way. . .

Yeah, the 6'4" 250lb dude's knee is lined up with your crotch.  The result of the crash is a direct blow to the nuts at full speed by a linebacker-sized guy's knee.

That's why you're in the ER today.  And that's why I've rarely felt so much empathy for any of my patients. . .