Man tased 15 times by lady cop

Officer Becky Sotherland of the Oglala Sioux Tribal Police is a dedicated civil servant. A less dedicated cop would not have the persistence to taser an unresponsive man 15 times. At the beginning of the video a woman can be heard saying “This is the thirteenth time tasing him.” Another bystander states, “We’ve been watching him for about a half hour.” Obviously distressed, the woman says, “Oh my god… poor guy.” The other chimes in, “He probably can’t get in because she tased him so much.”
Eventually the bystanders intervene and help kindly officer Sotherland get the man into her car. The victim was charged with “suspicion of disorderly conduct,” trespassing, and resisting an officer. Suspicion of disorderly conduct? WTF! Sotherland's chief excused her actions by saying she was trying to get the man “to wake up and stand up.” The man, he said, was “lying on the ground, probably passed out, clearly intoxicated.”
If someone is not resisting what is the justification for the use of force? The FBI and Bureau of Indian Affairs are both investigating the incident.