A sieve is actually a filter with many holes used for strainging water and liquid from something. The chant is directed to the goalie to say that he/she lets up a lot of goals because he/she is a sieve and contains many holes.
In other words...the goalie sucks
The goalie let up 5 goals that period, what a siv.
Crowd chant after a goal "SIV!! SIV!! SIV!! SIV!!" (directed to goalie who allowed the goal)