The Big Bang Theory is a more recent example.
Prior to mid-2015, Nine had the sole FTA rights to the show, and aired it a lot across the main channel & Go! (now 9Go!). At the time, the ratings for the show were quite high.
However, in May, it was reported that Nine had cut back its output deal with Warner Bros, who distributes the show.
As a result, Seven picked up Seasons 1-7 of the show, who commenced airing them from October that year, just as Nine, who maintained its first-run rights, started airing new eps from its then current 9th season. Nine also retained repeat rights to Season 8, before Seven picked it up a year later. There was also a time when both networks aired the show simultaneously, albeit with different eps from different seasons.
After September 2017, Seven stopped airing repeat eps of The Big Bang Theory, and by early 2018, Nine regained the repeat rights to the earlier seasons, therefore becoming the sole FTA broadcaster of the show once again, with older eps airing on 9Go!.