This is a juvenile Green Anole. He is just barely over 2 inches (5cm) long, head to tip of the tail.
Wikipedia has this to say about Green Anoles:
Anoles are territorial creatures. Some have even been witnessed fighting their own reflections in mirrored glass. Stress in an anole can be identified by several symptoms, to include chronic lethargy and persistent black semicircles behind its eyes. Like many lizards, anoles display autotomic tails, which when broken off continue to move. This hopefully distracts the predator and helps the anole to escape.