For group exercise classes, where there is a large group of people and I haven’t assessed any of them, I follow the AFAA and ACE rules on contraindications for group exercise classes.
For personal training, I look at the goals – short term, long term, and function – of the person I’m training. I might have an individual do a movement that is contraindicated in a group-ex class, but if it supports their daily activity or sport. Although it happens occasionally, I don’t typically train competitive athletes for sports performance. I train regular individuals who might include a sport as recreation but are interested in sustainable health.