Two points. First, by "jeans" we all mean "denim", not the way the pants are cut, right? I have moleskin "jeans", for example, that are perfect with a tweed jacket.
Second, as someone else pointed out, it depends a lot on the sports coat. I suggest a variation of Fuuma's rule about wearing sneakers. If the sports coat looks like something you might actually do some sort of sport in, e.g., a long walk, it will work with jeans. If it doesn't, it won't.
For example, a corduroy jacket works perfectly. Something with a self-stripe? Probably not. For this reason, I really don't like the velvet jacket + jeans look. I find it too intentionally edgy, sort of like the people who wear tennis shoes with DJs.