Sack Ya Nuts refers to the failure of a task, this is commonly used when someone gets killed in a clutch situation when its a 1v5, there are different variations for this depending on if the failure happened in the past or present or if it happened to you or another person.
Man I was in duos for Black ops 4 blackout and my teammate sacked his nuts.
My mates such a bloody wanker he bought a PS4 instead of a PC I knew he would sack his nuts.
Oi mate you got a assessment due soon you better not sack ya nuts.
Damn bro I was on a 500 combo on love live school idol festival but then I sacked my bloody nuts and missed a note.