Fatigue reduces both strength and accuracy. There's a physiological reason why tiredness weakens muscles. Muscles are made up of thousands of fibers. Each fiber stores sugar. and when it runs out of its stored sugar, it cannot contract effectively. As you tire, your muscles have fewer fibers to contract and you become weaker and less coordinated. This means that a pitcher who is warmed up and fresh will have more active fibers in his muscles and be able to throw more accurately and faster than when he is tired. A fresh football player can kick further and more accurately than when he is tired. That's why professional and college sports teams have large rosters, so they always have plenty of fresh players.
The same principle applies to boxers, wrestlers, tennis players and so forth, but they do not have the luxury of calling in a substitute. If you compete in an individual sport that requires both endurance and coordination, take it easy early in your competition and save something for the end. For more information on sustaining strength and coordination see my report on Carbs for Endurance