Does the ending suggest ...
That Harry might have found a new passion in his life --- coaching youth baseball?
Because when he tosses the ball to the kid, the kid asks, "Why'd you do that" and Harry responds, "Just thought you shoulda seen it once." The kids were also clearly impressed with his throw, as they shouted "WOW!"
Also remember that he goes to watch the kids play right after he watches the "Save the Tiger" poster. That would suggest that his goal in watching the kids play was to impart his knowledge about baseball to them, to preserve all that he knows just as environmentalists want to "Save the Tiger." The night before, he also had fun with the young girl, showing that interacting with youths might not be a bad idea for him.
And I know the kid says, "Mister, you can't play with us." But Harry pointedly doesn't leave; he stays to watch.
I like to think that Harry realizes the need to start looking forward, not backwards; and he needs to set a goal for himself. That goal, reasonably, might involve baseball, which is his passion.
Thus, I think the ending is happy conclusion, indicating that Harry is beginning a new career / hobby as a baseball instructor to youths.