A bit of simple GCSE level physics, but explained in a rather roundabout way:

If a ball travels approximately horizontally towards a static object (lets say a horizontal bar) and hits the underside of said object, this will cause the ball to have backspin as it falls sharply downwards.  Then, if as the ball comes down it comes into contact with a flat horizontal surface soon afterwards (the ground, say) the backspin will make it bounce backwards a bit in the direction of the horizontal plane from which it came.  So, if it hits our static object (the bar) again upon bouncing up, and if we imagine there was a straight line (let’s say it’s white) on the floor immediately below our static object (the bar), it must have hit the ground beyond that line.  If it hadn’t landed beyond the line, it would have missed the bar on the way back up.

"maybe nobody will notice, after all the're aren't many cameras around" - Manuel Neuer

Basically, what I’m saying is, the ref and his assistant could have figured out the ball had crossed the line simply from the fact that it hit the bar again as it bounced up.  “Get over it” I hear you say.  Maybe one day…

Here’s what I played tonight:James Yuill – “My Fears” (LP – “Movement In A Storm”) (Moshi Moshi)
Micah P. Hinson – “Watchers, Tell Us Of The Night” (LP – “Micah P. Hinson and the Pioneer Saboteurs”) (Full Time Hobby)
Harold Nono and Hidekazu Wakabayashi – “Let’s Go Find Mushrooms” (LP – “Harold Nono/Hidekazu Wakabayashi”) (Bearsuit)
HEALTH – “USA Boys” (single) (City Slang)
My Jerusalum – “Boom! Boom! Boom! Goes The Trolley” (single b-side – “Love You When You Leave”) (One Little Indian)
Wildbirds & Peacedrums – “Fight For Me” (EP – “Retina”) (Leaf Label)
Jaga Jazzist – “Touch Of Evils (Cuckoo Mix)” (EP – “Bananfluer Overalt”) (Ninja Tune)
Oh Ruin – “The Pillow Where Your Head Does Lay” (single) (Static Caravan)
Uffie – “Hong Kong Garden” (LP – “Sex Dreams & Denim Dreams”) (Because)
David Karsten Daniels & Fight The Big Bull – “Die And Be Buried” (LP – “I Mean To Live Here Still”) (Fat Cat)
Carlou D – “Yaaboyo” (LP – “Muzikr” (World Village)
Tender Trap – “Do You Want A Boyfriend?” (single) (Fortuna Pop!)
Grasscut – “In Her Pride” (LP – “1 Inch / 1/2 Mile”) (Ninja Tune)
Pulled Apart By Horses – “Back To The F**k Yeah” (single) (Transgressive)
Archie Bronson Outfit – “Hoola (House Of David Remix)” (single b-side) (Domino)