How to delete rows from a dataframe?

i have a dataframe of thousands of rows, called df1. it has several fields, field1, field2, and field3
i want to delete all the rows where field2.count() < 100 (grouped by field 1)

i have a dataframe defined as: filter = df1.groupby(‘field’).count()>100 where there are a few rows where the count <100

how do i drop the rows i am not interested in?