I've gone to a number of concerts in the decade since my tinnitus got worse, and will probably go to one next month -- no problems for me, though, there are certainly shows that I tolerated in my youth that I would just walk out of now, earplugs or not.
It really depends on the show. Is it a laid back rock band in a venue with a double high ceiling and a reasonable audio engineer, keeping average volumes in the 85-90db range with occasional spikes to 95? You're almost certainly fine with earplugs. Is it an insane EDM bass show in a basement club with average volumes in the 110-120 range with spikes to 130? That's probably not safe for anyone.
The audio estimates in the engineer's story from
@Michael Leigh 's post above are
much higher than what I've clocked at actual shows with a dB meter over the last few years, but that just speaks to the variation in venues and kinds of events. Your average indie rock show in a midsize venue (or even better, outdoors) is not going to have sustained 100db volumes unless you're standing right next to a speaker. But, a Skrillex show in a concrete basement? It might!
The last show I went to (The Mountain Goats, yay for goats) was basically the same volume as when we saw one of the recent
Star Wars movies in a normal theater. The next show I'm likely to go to is Kurt Vile, who himself has tinnitus badly enough to have written music about it, so you'd assume he hires reasonable audio techs, but time will tell...
I don't know much about sporting events but I have read some things which lead me to believe that large, fully packed football stadiums may be as loud or louder than the typical concert. In practice I've only gone to basketball, hockey and baseball games, all of which have been fine with earplugs.
tl;dr the safest thing to do is to just not go to concerts, but also the safest thing to do is basically never leave your house or ride in cars or drive motorcycles, so you have to figure out which of these things are worth rolling the dice and which are not.