There are some notorious users who destroy the leaderboards. With swimming it would be easy to implement to filter it out. If the avg pace is faster than the actual world record, it is definitely false recording/wrong activity type/bad joke/etc.
Just for help, the actual pace of WR for 50m freestyle is 40.32 sec/100m (50m WR is 20.16)
The swim challenge leaderboard look like this now:
And the false users activity, you can see, avg pace is 0s/100m:
I will flag this activity, but I am fed up with this guys notorious recordings. I would be happy if he/she would not join the challenge or the leaderboard would be clean of these crap.
Also if Strava wants to look serious, it should ban all of these things, as it makes the whole challenge/leaderboard/social thing look like a bad joke. Who wants to subscribe to a bad joke?