ZHANGJIAKOU, China—Freestyle skier Jon Sallinen’s first run in Olympic halfpipe qualifying Thursday wasn’t picture perfect. He drifted out of the halfpipe and collided with a cameraman. Collarbone aching, the 21-year-old from Finland picked himself up and tried it again in run No. 2—only to fall once more and have to make the walk up the pipe to retrieve one of his ski poles. All just a snapshot of a dangerous sport that leaves most of these athletes with scars, both inside and out. Sallinen’s wrecks during the qualifying round gave the day’s leader, Aaron Blunck, flashbacks to his own crash in the halfpipe 16 months ago, when he broke six ribs, fractured his pelvis, lacerated his kidney and bruised his heart by landing on the pipe’s cold, unforgiving edge. “I cringed on the inside,” explained Blunck, who was one of four Americans to make it to Saturday’s final. “I get …