Swipe to the left at the "Squad" screen to select a formation. When an exclamation mark appears on a player jersey, it indicates that they are in the wrong position. Tap and drag players into their correct positions. To find the correct position for a player, tap and hold their jersey and drag them to a position that has a lighter background. You can also view their condition, morale, and quality by tapping the drop-down option at the lower right corner. When a player's health is low, he has a better chance to get an injury in an upcoming match. Try using a 4-4-3 or 4, 1, 3, 2 formation to have a defense with at least three players to defeat weaker teams.