How to counter LeBlanc
Let us take a look on how to beat LeBlanc. We will look at champions who are strong against LeBlanc and who are weak against LeBlanc. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Mid champion who counters LeBlanc. You can already win in champion select with the right counters for LeBlanc. If you want to know how to counter LeBlanc then you need to take into account the best picks vs LeBlanc and the worst picks vs LeBlanc. This LeBlanc counter data is based on matches played by Pros on patch 13.24 and previous ones. It is important to see whether Pros counter picked LeBlanc or whether they played as LeBlanc.
Champions used by Pros to counter pick LeBlanc
Looking at the matches from Pros (see table Pros counter picked LeBlanc) we can see that they picked 
Akali most often to counter pick LeBlanc. The matchup Akali vs LeBlanc occured 32 times. LeBlanc has 18 wins and 14 losses in this matchup. Learn how to counter pick Akali to get another perspective on the data.
Lane outcome for LeBlanc
When looking at LeBlanc 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 LeBlanc. The lane outcome of LeBlanc consists of three outcomes: Win, Loss or Draw. Let's take a look of LeBlanc 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 LeBlanc.
Conclusion
Analyze the available data and learn how to beat LeBlanc. To master LeBlanc take also a look on LeBlanc builds and runes for LeBlanc. Good luck, Summoner!