How to counter Leona
Let us take a look on how to beat Leona. We will look at champions who are strong against Leona and who are weak against Leona. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Support champion who counters Leona. You can already win in champion select with the right counters for Leona. If you want to know how to counter Leona then you need to take into account the best picks vs Leona and the worst picks vs Leona. This Leona counter data is based on matches played by Pros on patch 14.12 and previous ones. It is important to see whether Pros counter picked Leona or whether they played as Leona.
Champions used by Pros to counter pick Leona
Looking at the matches from Pros (see table Pros counter picked Leona) we can see that they picked 
Nautilus most often to counter pick Leona. The matchup Nautilus vs Leona occured 64 times. Leona has 39 wins and 25 losses in this matchup. Learn how to counter pick Nautilus to get another perspective on the data.
Lane outcome for Leona
When looking at Leona counters you will notice that win rates alone are not conclusional. Therefore we provide an overview (see table Lane Outcome) where you can see the lane outcome of Pros who played Leona. The lane outcome of Leona consists of three outcomes: Win, Loss or Draw. Let's take a look of Leona lane and match outcome for specific matchups. Considering the lane outcome and the match outcome of a specific matchup, might enable you to find the right counter for Leona.
Conclusion
Analyze the available data and learn how to beat Leona. To master Leona take also a look on Leona builds and runes for Leona. Good luck, Summoner!