In Sonic Rumble, your Season Leaderboard score is the total of all scores you've collected from battles throughout the season, except for those from 'Challenge Battles' and 'Custom Matches'. 

Plus, you can boost your score with nifty "score bonuses" like "emotes," which you can tweak from the customization screen, will give your ranking an extra edge!

Related FAQ
How can I check the score bonuses I have activated?