How to counter Trundle
Let us take a look on how to beat Trundle. We will look at champions who are strong against Trundle and who are weak against Trundle. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Top champion who counters Trundle. You can already win in champion select with the right counters for Trundle. If you want to know how to counter Trundle then you need to take into account the best picks vs Trundle and the worst picks vs Trundle. This Trundle counter data is based on matches played by Pros on patch 14.21 and previous ones. It is important to see whether Pros counter picked Trundle or whether they played as Trundle.
Champions used by Pros to counter pick Trundle
Looking at the matches from Pros (see table Pros counter picked Trundle) we can see that they picked 
Gnar most often to counter pick Trundle. The matchup Gnar vs Trundle occured 5 times. Trundle has 4 wins and 1 losses in this matchup. Learn how to counter pick Gnar to get another perspective on the data.
Lane outcome for Trundle
When looking at Trundle 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 Trundle. The lane outcome of Trundle consists of three outcomes: Win, Loss or Draw. Let's take a look of Trundle 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 Trundle.
Conclusion
Analyze the available data and learn how to beat Trundle. To master Trundle take also a look on Trundle builds and runes for Trundle. Good luck, Summoner!