Transperth transit (Perth, Western Australia) provides free transit to certain events, like the Red Hot Chili Peppers concert on 2/12/2023

Flyer on a UTA bus.

In the US, arenas in Phoenix, Seattle, and San Francisco include free transit for ticketed events, not just for sports teams but concerts too ("Seattle Kraken expansion hockey team sets new standard for transit benefits in transportation demand management: free transit with ticket").  It depends on the agreement for how many transit services/modes are covered.  For Seattle it's all but ferry service.

The baseball and football stadiums in Pittsburgh are in a special free transit zone that was initially supported by the teams, but now is paid by a parking structure company and a casino.

University of Utah sports events include transit service in the tickets, and this week, with the NBA All Star Game in Salt Lake City, Utah Transit Authority transit services are free ("UTA offering zero fare, extended hours for NBA All-Star weekend,"KSL-TV) with some 24 hour service and expanded service.

That's pretty cool, although last year, the entire month of February was free transit on UTA.

This ad was in a Reddit thread.  

It's already gone from the Transperth website because the concert was on Sunday.  

By contrast, apparently Public Transport Victoria (Melbourne) promoted transit to their concert too, but didn't provide expanded services and there were serious problems ("‘Awful planning’: Unofficial Red Hot Chili Peppers concert after-party lifts commuter spirit," News.com).

But looking at the authority's special events page, a number of future concerts at a variety of venues also have free transit service.

Transperth also offers the "Suburban Event Bus Network" to provide extended service after events end, which few US transit systems offer.

Optus Stadium, where the Chili Peppers played, has a nice webpage on transportation options.  It's pretty much better than any such page I've come across in the US. 

More communities need to build special event transportation into their planning and contractual agreements for stadiums and arenas, not just for sports events, but also for concerts and other ticketed events. 

Parking around Miller Park stadium in Milwaukee.  Photo via Milwaukee Business Journal.

A number of transit authorities do provide special transit service for sports events and sometimes concerts, but it isn't free.

A number of arenas and stadiums are well located for transit service, and as a result may have more than 50% of total trips to and from the facility realized by transit, which significantly reduces the negative effect of trip demand.