The idea of having an injection of "platelet-rich plasma" sounds as far from fun as one can have in the realm of injections. But what is "platelet-rich plasma" therapy, which outfielder Carl Crawford just had on Thursday? Manager Bobby Valentine told all yesterday he is not a reliable witness. "I'm not an expert, but it's a shutdown thing — it hurts a lot when you get it," he said. "It's not like you get it, and then get it again and think you can pick up where you were. From what I understand, it goes in there and then it kind of feels thick because it's gooey stuff that's in there doing whatever the hell it's doing. And then once it lubricates up, then you can start going again." OK, time to explain. Crawford has a sprain, or a small tear, of the ulnar collateral ligament in his left elbow. This is the same ligament that when torn more significantly requires reconstructive, or Tommy John, surgery. Because there is little blood flow in the area of the UCL, there is less chance the healing properties of blood can get to the area of the tear and go to work, or at least not that quickly — unless you go to the site of the sprain (tear) with a needle and squirt the area with a dose of your own blood.