As a machine learning researcher, I know that I have different tools at my disposal:

[...]

  awk '($(NF-1) = /Ban/){print $NF}' /tmp/fail2ban.log \
  | sort                                             \
  | jdresolve -                                      \
  | uniq -c                                          \
  | sort -n -r                                       \
  | sed -e 's/^[ \t]*//'                             \
  | sed -e 's/ /\t/'                                 \
  | head -n 100

:)