There are a couple of ways to handle this:
- Whenever a teammate boots a routine grounder, scream their name at the top of your lungs, and tell them how bad they are. Stomp around the mound with steam coming from your ears, and huff and puff your way to the rubber. Come set, then turn and throw the ball to first with all the speed and accuracy that your rage can muster. Stomp back to the rubber and yell at the 1st baseman for missing that ball you just threw in the dirt 10 feet wide of the bag. Lose all semblance of control, and have a total meltdown on the mound.
This will ensure that you never again have to deal with these teammates when you're pitching. Because chances are real good you'll never get the chance to pitch again.
2. Whenever a teammate boots a routine grounder, just turn to accept the ball from your infielder. Keep your chin high and your face and body relaxed. Have a quick conference with your SS and 2b to discuss how you're going to work on the next hitter, and whether you can either pick off the runner at first or get the hitter to hit into a DP. Remember that once you deliver the ball, you can't control its direction. Get the sign, nod, and go back to work.
This will ensure that your infielders don't quit or give up; that they know you still have faith in them; that you are someone they can have faith in; and that you are all in this together, win or lose.
It will ensure that everyone watching, from your present coaches, to umpires, parents, opposing players, and perhaps some day scouts and potential future coaches, see that you are mature and relaxed, capable of performing your best even when others fail to.
It's your choice how you react, and how you present yourself to the world. Remember, people can always identify a winner, even if he is on the losing side that particular day. And when you return to the dugout, your teammates can tell that you are a winner when you approach the kid who booted it and tell him that he'll get the next one...and you believe it, no matter how many he mishandles.
Hang in there, kid!