So basically we have to earn S- to S+ on a champ to get a free chest, i get that. So i take it's just on champs we don't have any S ranks on? What's the point of enforcing a weekly limit? Maybe it's just the random ramblings of a not so great player. Feels silly to me. [slayer-jinx-unamused]
If you go to champions, on your profile page, it should tell you when you scroll over a champion if you received a chest for them or not. It doesn't matter if you've gotten any ranking before then. If you own a champion, have not gotten a chest with them for the season, and get a new s-,s,s+ rank, and have a chest available, you should receive a chest. So weekly champs don't work, unless you own a champ that is in the free weekly. Here's an example of it showing a chest aquired :). I hope this helps.
Own a champ, have a chest available, get a s- or higher grade with them! 1 chest per champion per season, I believe. https://s32.postimg.org/fn3rkmw85/Chest.png Ahri, Annie, Ashe, and Azir have a special boarder, that will tell you if you have gotten a chest for them or not.
