Through item boxes. I'm fairly sure it's a legendary item and there's 1% chance of getting a legendary item in the items box. So it's going to take a long time to get one ^_^

starwa7s is right, this is the "Spider" torso, which is a LEGENDARY item that has a lot of hp and pretty good resource stats.
And as starwa7s said, through normal item boxes you have %1 chance of getting a LEGENDARY per item, which makes it pretty difficult to obtain a specific LEGENDARY item (there are more LEGENDARY items, and mostly, they are more useful than the more common items(EPIC,RARE,NORMAL)).
If you use tokens to get silver or golden item boxes though, the chance of getting LEGENDARY per item increases to %5 and %7, respectively(these boxes also give u 5 items per box instead of 3 items per box,which further increases the benefits you get from the boxes-more RARES,more EPICS, more LEGENDARIES )
Also the golden box is guaranteed to give you items with at least RARE rarity.
P.S. Except for NORMAL items, you can get items only from item boxes(you can also buy the NORMAL items from the shop anytime,provided that you have enough credits)

that is the spider torso. the best one, besides gladiator lvl 30

Only if you're using energy shield