If a size 5 football(soccer ball)-sorry!
is inflated a bit too much and happens to be in a pressurised plane, could it explode?

If the plane is pressurized to the same ambient pressure as that in which the ball was originally filled, it would not explode.

Ah but fred, I had a sealed pack of crisps(or chips fred,as you might know them) on-board a flight and it expanded almost to bursting point, thus if the pack was already inflated before the plane pressurised, would we see a "ka-boom" at mini scale?

hmmmm.....an expanding crisp bag and an exploding football? slightly different skins dont you think/ not being a scientist on this matter i have an idea that the impact from a booted foot travelling at "x"m/s would be greater than the atmospheric pressure inside an aircraft. you said it,if it can't pop a snack bag what chance a football?

The inside of an airliner is pressurised to an equivalent pressure that would be found at 8000 feet, so it is slightly lower that the air pressure at sea level - it's a compromise, they do this to lessen the strain on the aircraft structure while keeping it at a level that the passengers would find comfortable - if they had to keep it at a sea level pressure, they'd have to increase the strength of the aircraft, this would increase the weight & make it less profitable to run.