In other apps when you tap on a tab button it will perform a function (ex: Instagram: search for a user, click their profile, click search tab button takes you back to the initial search screen).
When you click the tab button while in a nested scene for that tab, you should go back to the root scene (ex: Scores screen -> game -> boxscore -> * tap scores tab button * -> back to Scores screen).
Something along the lines of the following would go in navigationOptions({...}) of the tab navigator:
tabBarOnPress: (scene, jumpToIndex) => {
console.log('onPress:', scene)
}
source: https://reactnavigation.org/docs/tab-navigator.html#tabbaronpress