This is a Cicada Killer, a common wasp out and about this time of year. Its behavior suggests it is a male, which monitor their territories for intruders (of any size!) and can bluff-charge in defense. Males cannot sting; females tend not to defend their nest burrows (which they use individually, not in a colony) in this way, if at all. Cicada Killers are harmless unless you happen to harass or handle a female, and busy themselves with hunting cicadas with which to provision their burrows.
These page provides more information on the life cycle of these large insects: