The current version of League Standings was developed and tested one WP 3.5.1. If you use older version of WordPress, good luck! If you are using a newer version of WP, please let me know how the plugin works, especially if you encounter problems.
Upgrading to this version of League Standings should not impact any existing schedules. (But backup your DB before you upgrade, just in case. 🙂 NOTE that it will overwrite the css folder and the plugin’s stylesheet – mstw-ls-styles.css. So if you’ve made modifications to the stylesheet, you may want to move them to a safe location before installing the new version of the plugin.