i was sitting at 916 ish which was enough for 11th place, decided id unshield play 2 or 3 quick round before i come up as target and reshield, probably get top 10. duing my first round i come back to an entire screen of me getting demolished.
just wanted to share my sad 
Yeouch! What team were you using?
yup this happened to me during the last heavy metal tourney needless to say if i get past 900 i make the investment on a better shield now
Sometimes it does seem that there are spies out there that wait for you to unshield and then tell all their friends to attack you at one time.
If someone’s in the same bracket as you they can tell when you unshield if you’re on their list, though I doubt most attacks are more planned out that skipping through your queue.
I had the same issue during the last hulk tourney, my level 80 hulk was smaller than everyone else’s so I unshield for a match, pop up in everyone’s queue at once. Lost 200 points, and then shielded another 20 attacks -.-