The right choice would be "The coach, an expert in the sport, explained the revised rules to us."
One that is general, and does not specify which specific aspect you are looking in to
Tecumseh was a native American Chief of the Shawnee tribe. He was born in 1768. He decided to become a warrior after his father was killed in 1774 by white men who were violating a treaty by entering Shawnee land. By becoming a warrior, he felt he could defend his people and their land.
She is completing her degree this year.