To block incoming ssh connections, edit the /etc/pf.conf and add the following line at the bottom:

block in log quick proto tcp from any to any port 22

You can use vim or use something like this:

sudo sh -c "echo 'block in log quick proto tcp from any to any port 22' >> /etc/pf.conf"

Then reload the pfrules:

sudo pfctl -Fa -f /etc/pf.conf

For this to work the firewall must be enabled.

Example of how file looks after the rule has been added: cat /etc/pf.conf

#
# Default PF configuration file.
#
# This file contains the main ruleset, which gets automatically loaded
# at startup.  PF will not be automatically enabled, however.  Instead,
# each component which utilizes PF is responsible for enabling and disabling
# PF via -E and -X as documented in pfctl(8).  That will ensure that PF
# is disabled only when the last enable reference is released.
#
# Care must be taken to ensure that the main ruleset does not get flushed,
# as the nested anchors rely on the anchor point defined here. In addition,
# to the anchors loaded by this file, some system services would dynamically
# insert anchors into the main ruleset. These anchors will be added only when
# the system service is used and would removed on termination of the service.
#
# See pf.conf(5) for syntax.
#
#
# com.apple anchor point
#
scrub-anchor "com.apple/*"
nat-anchor "com.apple/*"
rdr-anchor "com.apple/*"
dummynet-anchor "com.apple/*"
anchor "com.apple/*"
load anchor "com.apple" from "/etc/pf.anchors/com.apple"

# block incoming ssh
block in log quick proto tcp from any to any port 22