Yes it is possible to eat too much salad.
However the worst thing that would happen from eating too much salad is that you may experience bloating, stomach pain, digestive issues, stomach cramping and possibly diarrhea.
If your stomach starts hurting then you're likely eating too many salads and should slow down on the amount of salads you eat.
Salads are very healthy for you and eating a bowl of salad per day or every other day is okay and will do you no harm.
But if you eat more than 2 or 3 bowls of salad everyday then it could cause those stomach issues.
But most people will maybe eat only 1 bowl of salad per day and sometimes only every other day.
But you can eat as much salad as you want too and your stomach will let you know when you're eating too much salad.