A video has been posted on The Telegraph's website showing a woman being thrown off a Ryanair plane by the Guardia Civil (the lowest level of police in Spain): Camera captures Ryanair passenger ejection for 'wrong hand luggage'.
It is understood that the passenger had a book and a scroll in her hand that she couldn't fit in her case, though the airline claims she pushed past staff without showing identification.
Ryanair has a history of being draconian with its baggage policies. The Irish airline was one of the first airlines to see the profit-making potential of ancillary fees and as a result made its baggage allowance smaller than any other airline in Europe to force people to check their bags and pay for the privilege.
I too have caught on my camera phone abuses of power by Ryanair-authorised airport staff. I saw a man's bag fit the airline's baggage allowance but still get forced to pay a fine as the soft material of his bag meant it was a struggle to fit in. See the pictures here: How Strict is Ryanair's Hand Baggage Policy?
See also: Ryanair Fees

Guardia Civil is not ‘low level police’. Guardia are a national force which police national crime and borders; unlike the police in Spain which deal with local, low level crime; directing traffic etc.
The ‘Guarda Civil’ had been associated with the Franco Regime during the Spanish Civil War, however times have changed and they should not be labeled as such in this time and age.
More thought into how information is relayed should be considered.
Why was my comment not displayed?
Simply, if they are so cheap because of a book, or a an inch over , they are not worth the hassle.