In seizing on rugby as a model, Atavus was choosing to highlight a sport in which tackling above the shoulder is not permitted; some players wear “scrum caps’’ but none wear the hard plastic helmets used in football; and the rate of concussions is lower than in football, according to Dawn Comstock, a sports injury epidemiologist at the Colorado School of Public Health.

But a year later, researchers at the Colorado School of Public Health concluded that the air quality around oil and gas wells puts people nearby at an increased risk of developing cancer. But the oil and gas rally brought out plenty of workers who called Colorado’s fracking industry the safest in the nation.

“Getting shocks at the end of life is not really helping patients live longer or better,” said Dr. Larry Allen, a heart failure specialist at the University of Colorado and an author of the study.