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The night began like many others for Roberto Chicas. But it ended far differently.

Two weeks ago, the 35-year-old San Francisco bartender finished a round of drinks with friends at the end of his shift and e-hailed an Uber car to take them all to their respective homes. UberX driver Patrick Karajah, 26, showed up.

As they began the trek home, the passengers started questioning Karajah's route, according to Chicas' attorney, Harry Stern. Karajah took the freeway, when the passengers wanted to take surface streets so they could be dropped off in sequential order. As they continued on the drive, Stern said, the dispute between the passengers and Karajah reportedly got heated.

"The driver got more and more agitated," according to Stern. Karajah allegedly "started saying things like, 'I'm tired of people who don't know where they're going. Maybe you guys should just get out.'"

Driving down the freeway, Karajah reportedly blew past the exit for Chicas' neighborhood and pulled off at an exit far from the passengers' homes, Stern said. At one point, they claim, he tried to force the passengers out of his car. He then reportedly drove 50 yards, then tried again to oust them.

At Karajah's second attempt, Stern said, Chicas and another passenger got out. The third passenger momentarily stayed in the backseat to make sure they didn't leave anything behind.

"All of the sudden [Karajah] appeared at the door with the hammer and said, 'I told you to get the f*** out of my car,'" Stern said.

Karajah then marched over to Chicas, clobbered him in the head with a hammer, went back to his car and drove off, according to Stern. Chicas was left lying on the ground, bleeding and drifting in and out of consciousness. It's still unclear if Chicas will regain vision in his left eye, Stern said.

The Uber driver was charged with assault with a deadly weapon and battery with serious bodily injury. He has pleaded not guilty to both counts, according to the San Francisco District Attorney's Office. He was freed on $125,000 bail. Karajah's attorney declined to comment.

When Uber was asked to comment on this incident and to detail the protections it offers passengers, a spokesman didn't comment on this specific case. The San Francisco-based company says it puts an emphasis on safety.

"Safety is our top priority and foundational to the Uber experience -- for both riders and drivers -- and we take any potential breach of safety seriously," the spokesman said. "We will always work to improve and increase safety measures, and with unprecedented accountability built into the app, Uber continues to connect riders and drivers with the safest rides on the road."

What do you agree to when you use Uber?

What makes this more than just an altercation between driver and passengers? An Uber ride is different from hopping into a taxi. When you download Uber's app and get into a car summoned with the mobile reservation system, you agree to a host of terms and conditions by default. And Uber is young enough that situations like this one are still largely uncharted territory.

Since Uber launched five years ago, it's grown rapidly. It now has cars driving around 204 cities in 45 countries, and the company claims to cover 55 percent of the US population with its offering. It's also the highest-valued venture-backed company in the world right now, with a valuation of $18.2 billion.

Like its rivals Lyft and Sidecar, Uber is a so-called ride-sharing service that puts potential drivers through a background check so that they can become an impromptu taxi driver using their own car and Uber's tech platform. For each ride a driver carries out, Uber gets a cut of the fare -- typically between 20 percent and 25 percent.

Uber

The alleged incident between Karajah and Chicas wasn't the first conflict between an Uber driver and a passenger, and it's unlikely to be the last. But the outcome of this altercation may help clarify Uber's responsibility to passengers.

What exactly do passengers agree to when they use Uber? That depends on whom you ask.

"People don't know what they're getting into when they get into one of these cars, they don't know what they're getting into when they download the app," said lawyer Chris Dolan of Dolan Law Firm, who is representing a 6-year-old girl struck and killed by an Uber driver earlier this year. "They're giving Uber a free pass -- up to death."

Dolan claims Uber's terms and conditions are a way for the company to absolve itself of any liability in cases of injury or accident and to avoid responsibility for a driver's actions. "It completely covers their ass and says 'We're not responsible for anything that happens to you, period,'" Dolan said. "It says, 'You can be raped, you can be killed, you can be murdered, and it's not our responsibility.'"

When asked about the protections Uber offers passengers, an Uber spokesperson pointed CNET to its webpage on safety. The page details the background checks drivers go through -- which require county, state and federal checks that go back seven years -- and the $1 million liability insurance they must carry.

Uber CEO Travis Kalanick has heralded the service as being ultrasafe. "Safety is No. 1 at Uber...so we make sure the system is in place so riders get the safest ride possible," Kalanick told CNNMoney in June. "With that said, Uber is in the limelight. When things happen, if there's claims of any kind in any city in any car, we take those claims very seriously."

Dolan believes Uber's statements on safety contradict its terms and conditions. "It's an outright deception on people," Dolan said. "They do not in any way seek to warrant that their product is safe. They put it right there in the writing."

The fine print of Uber's terms and conditions clearly says that passengers accept a risk by using the service.

"You understand, therefore, that by using the application and the service, you may be exposed to transportation that is potentially dangerous, offensive, harmful to minors, unsafe or otherwise objectionable," Uber's terms and conditions read, "and that you use the application and the service at your own risk."

A look at Lyft's terms of service shows it operates nearly the same way. "Lyft has no responsibility whatsoever for the actions or conduct of drivers or riders," the terms of service reads. "Responsibility for the decisions you make regarding providing or accepting transportation rest solely with You... Drivers and riders use the services at their own risk."

Legal analyst and ex-prosecutor Steve Clark said that Uber and Lyft are basically trying to show through these terms of use that they are ride-matching services, rather than transportation companies. (He is not representing any passengers in lawsuits with Uber or Lyft, and he hasn't advised either company). If they can prove they are merely tech platforms, he said, they may be able to protect themselves from some lawsuits. Yet, Clark said, "it remains to be seen if their terms of use would be enough to shield them from liability."

A parallel could be drawn with online dating services, which faced their own liability challenges early on. In one high-profile incident in 2011, Match.com was sued by a woman who claimed she was sexually assaulted by a date she met through the service. That lawsuit concluded after Match.com began screening its members for sexual predators.

Are ride-sharing passengers out of luck?

Though the vast majority of Uber and Lyft drivers are safe, courteous and competent, several incidents have occurred during the last year that have called into question the safety of the services. The most severe incident was the death of 6-year-old Sophia Liu, who was struck and killed by an Uber driver on New Year's Eve in San Francisco. There have also been more than a dozen allegations of sexual assault and groping; kidnapping; and physical assault, according to several media stories.

Uber

Even though Uber covers itself with its terms and conditions, Clark said Uber could still be held responsible for the hammer attack. "This appears to be a dispute about the route, and Uber will probably be on the hook for that," Clark said.

When Karajah began driving for Uber, he had no criminal record, according to the San Francisco District Attorney's Office. Even so, Uber still may be accountable for Karajah's alleged actions if it's proven the company didn't adequately train him in how to deal with conflicts with passengers, Clark said.

"The question isn't only did he have a clean record, but how well was he trained," Clark said. "Just doing a background check and saying, 'You're on the way,' is not enough. You need some guidelines saying 'This is how you treat unruly passengers.'"

Uber declined to detail the training its drivers go through.

Uber drivers are classified as independent contractors, rather than employees, which could protect Uber from liability, Clark said. But the company's terms and conditions could be trumped in court if it's shown that Uber exercises a certain amount of control over its drivers and they are akin to employees. Such factors of control include the ability to hire and fire drivers, decide where their services are performed, or provide them with specialized equipment, along with other considerations -- many of which, some would argue, Uber has.

"The problem for Uber is the more control they assert, the more likely these people are going to be characterized as employees," Clark said. "It's kind of a double-edged sword for Uber. If it doesn't do training, it could be held liable for other reasons."

What about taxi safety?

No transportation service can guarantee that attacks won't happen. But if something terrible occurs, a passenger may receive monetary compensation without having to go through a legal nightmare to get it, depending on the type of insurance coverage a given service has.

Victims of assault can sue individual drivers, but they're likely to get more adequate compensation if they go through the company that arranged the ride in the first place, said Dave Sutton, spokesperson for Who's Driving You, an advocacy association for taxicab, limo and paratransit services.

While there are risks in using Uber and Lyft's service, are cabs any better?

Taxi drivers have assaulted passengers. The difference, Sutton said, is that cab companies are usually accountable in such instances.

Regulations for taxi companies vary from city to city, but all cab companies must have liability insurance of at least $250,000. The key, however, is that most taxi companies also have a backup umbrella policy to cover rare occurrences, like a passenger slipping on ice or being attacked by a driver, Sutton said.

San Francisco's Municipal Transportation Agency says on its website that the insurance that city cab companies carry means "when you hire a San Francisco taxi, you have proper legal recourse should the need arise."

While Uber requires its drivers to have $1 million of liability insurance coverage, which is higher than many cab companies, it's unclear if this would cover incidents like a driver attacking a passenger. This type of insurance coverage is typically meant for car accidents.

Uber declined to say whether Karajah's insurance would pay for the costs of the alleged incident with Chicas.

Uber's insurance adjuster has contacted Stern regarding the injuries that Chicas suffered, Stern said. He's waiting to see whether Uber will "come to the table and accept responsibility." If it doesn't, Stern said, he's prepared to sue.

"I'm not one that wants to stifle technology, by any means," Stern said. "But [Uber] just wants to reap all the profits and not be responsible when things go bad."