There is one way to frame motivation that I really like, that paradigm (or model) is one that compares intrinsic motivation to extrinsic motivation. "Ok coach, you are starting to lose me here"...hang tight it just seems more confounding than it actually is.
Extrinsic motivation is the one I'll start with. It's a little hairy but not necessarily all bad, and can be useful at times. Extrinsic motivation is when your drive to do something comes from an external stimulus. I either want to do it for an external reward (trophy, scholarship, bragging rights, being able to beat someone else, etc.) OR and this is where a lot of people miss the big picture...external FEAR ("I better do this or someone is going to yell", or "if I do this wrong I'm going to have to run sprints"). Some studies have shown that if you take people who already value something, and constantly offer them external fear OR reward, they begin to not only devalue or lose interest in the fear/reward, but they begin to devalue the ACTIVITY itself.
We as a society have to be very careful with extrinsic motivational tactics. I would say that if you put fear (extrinsic motivation coming from outside of them) in to a baseball player you are going to have a player that not only does not reach their potential as a player, but starts to devalue the activity, negative thoughts and feedback loops develop in the player's mind. Not to mention they tense up in crucial situations. Bad, bad stuff.
Intrinsic motivation is when you want something so that the drive comes from within you, without any external stimulus creating that drive. In other words, I want to go sprint because I want to see how fast I can be. I want to go train in the weight room so I can beat my personal best, because I enjoy the challenge of doing so. This motivation means the drive and reward is already inside the player, because they value the activity, joy, and challenge of it. It's built-in to them already. Constantly driving to be their best regardless of what's going on around them, potential rewards (player rankings?), whatever anybody else is doing. The intrinsically motivated ones are the ones coaches have to pull the reigns back on sometimes. Their motivation comes from within.
So knowing the difference between intrinsic and extrinsic, which one do you think produces better baseball players? Which one produces better PEOPLE? It's a very subtle difference but it is all around us, everyone is motivated for certain reasons, either internal or external. Awards, rankings, scholarships, are all side effects, not a means to an end.
When you get a young team it is so much fun because players are out there for the love of the game. When external motivators like trophies, playing time, social status get in the way, that's when things start to become more complicated. I have not seen a local adult league baseball game where players go out there because they have to, it's because they want to...and they pull hamstrings and roll ankles, and come back! They already have to work, it's a release to be on the field doing what they already love, because it's within them.
Can you get the player to value the sport on it's own? Chances are they have before. Chasing awards, stats, etc can be a real uphill battle. Show me a player that is intrinsically motivated, and I'll show you a player who will likely reach their potential and enjoy every minute of it. These are the players that can become "stars", and they understand that wins, awards, trophies, etc, are all side effects of them being intrinsically motivated. A driver that's on their path.