N.B.A."s Concussion Policy Has Major Role in Knicks-Pacers Series Brent Smith/Reuters The Pacers' George Hill, who sustained a concussion on Thursday, became the first player to miss a postseason game under the N.B.A."s new concussion protocols. The policy states that a player who exhibits concussion symptoms must be removed from athletic participation immediately and cannot return until he is symptom-free and passes tests. Professional basketball players do not routinely collide at full speed, or fire small objects at one another with extreme velocity. They do not tackle, ram or body-check. Their heads may rise to startling heights, but they are not in harm's way as often as the skulls of football, hockey or baseball players. Concussions in the N.B.A. are therefore relatively rare. But now a playoff series might be determined by one. George Hill, the starting point guard for the Indiana Pacers, was held out of an Eastern Conference semifinal game against the Knicks on Thursday, hours after being told he had a concussion. Hill became the first player to miss a postseason game under the N.B.A."s new concussion protocols. Under the league's policy, instituted in December 2011, a player who exhibits concussion symptoms must be removed from athletic participation immediately. He cannot return to action until he is symptom-free and passes a battery of tests. The N.B.A. does not set a timeline for a player's return, and there is no telling how long Hill will be out. Concussions can last for days, weeks or months, and the recovery time varies from patient to patient. Kobe Bryant of the Los Angeles Lakers played three days after sustaining a concussion in the 2012 All-Star Game. Chris Kaman, a Dallas Mavericks center, needed four weeks to shake off the effects of a concussion this season. "Concussions are like snowflakes: every one is different," said Dr. Michael Collins, the director of the sports medicine concussion program at the University of Pittsburgh Medical Center. The right evaluation has to take place to figure out what systems are breaking down. The Pacers" medical staff is conducting those evaluations on Hill, the team's 27-year-old playmaker, whose recovery could determine the Pacers" playoff fate. Indiana leads the best-of-seven series, 3-2, with Game 6 on Saturday night in Indianapolis. Hill was expected at the Pacers" training facility Friday afternoon to meet with the team physician and to take another concussion test, Coach Frank Vogel said. The Pacers had not yet ruled him out of Saturday's game and had listed him as day to day. If the Knicks win Saturday, Game 7 will be played Monday night in New York. If the Pacers win the series, they will open the Eastern Conference finals Wednesday in Miami. Hill is a critical piece of Indiana's lineup. His absence was felt immediately Thursday night, as the Pacers" offense disintegrated in an 85-75 loss that allowed the Knicks to stave off elimination. Hill had scored a team-high 26 points in the Pacers" Game 4 victory Tuesday, despite taking a blow to the head in the first quarter from the Knicks" Tyson Chandler. Hill showed no obvious symptoms at the time, and he played the rest of the game. The incident itself was unspectacular. Hill was chasing Raymond Felton and ran into Chandler, who was setting a pick near the top of the key. Hill's head collided with Chandler's left elbow, and Hill fell to the court. It took three seconds before he got up, but he appeared fine otherwise. No foul was called, and the television commentators did not even mention the play. Hill practiced with the Pacers on Wednesday afternoon and flew with the team to New York. He did not complain of any symptoms until the flight. "He said his head was hurting," center Roy Hibbert said. I thought he had a migraine. It was not until Thursday, after Hill participated in Indiana's morning shootaround, that he apparently sought out the medical staff, which determined he had a concussion. The two-day lag is not unusual, Collins said. "It's more common than you can imagine, actually," he said, adding, "The symptoms can be very tacit, very understated." Many concussion patients have dizziness, headaches and nausea, the result of what Collins called "an energy crisis in the brain." The more a person exerts himself, the deeper that crisis becomes. The symptoms could also be set off by a busy environment, like an airport, a restaurant or an arena. "All of a sudden, that energy crisis gets worse and worse, and it can be a lot more noticeable to the athlete undergoing it," Collins said. The N.B.A. consulted with the players union before announcing its new concussion policy 18 months ago, after the 2011 lockout. Zach Schonbrun contributed reporting.