The Stride Drill is primarily focused on the ability of the fielder to catch balls on a dead sprint. Have your fielders line up about 40 or so feet out in front of you and about 40 or so feet to the left (or right). You will have three balls in your hands, and at your "go", the first athlete in line will sprint on a line that is parallel to you. You as the coach then get to play QB. You try to lead the athlete by throwing balls so they can catch them on the run. Tell your fielder that as they catch the ball, to just drop it immediately and find and react to the next ball which you will throw as they drop the previous ball. Do about 3 balls, if you do any more they end up getting too far away from you. Of course you can vary the distances . Then have them sprint back to pick the three balls up and bring them back to you and form another line on the right side (or left depending on which side you start from).
What I like to have them do, is to do about 3 or four of these as a group and then I tell them that I am going to challenge them. So when I throw the 3rd ball, I am going to try to throw it so they have to dive for it. The kids stop thinking they are tired and try to make a great play... its fun for them and they get a good workout in the interem.
At younger levels this is a great tool because a player's coordination is beginning to gel and it is difficult to run and do anything else at the same time. Youth coaches will relate that the younger kids have a hard time with their point of focus bouncing up and down as they run. This drill helps players to become more comfortable.