haproxy.conf

# At most 10 concurrent connections from a client
acl too_fast fe_sess_rate ge 10

# Matches any path beginning with a given prefix
acl bursts_inclined path_beg -i /client1

# Effectively working as a delay mechanism for clients that are too fast
tcp-request inspect-delay 1000ms

# Fast-path - accept connection if it's not this troublesome client
tcp-request content accept unless bursts_inclined too_fast

# The very fast client gets here meaning they have to wait full inspect-delay
tcp-request content accept if WAIT_END