This set was issued on the start day of the 8th Roller Hockey World Championship, which took place in Porto from 28 June to 7 July 1952. The tournament was won by Portugal, its 5th World Cup title, with Italy and Spain getting the silver and bronze medals, respectively.
Quad roller hockey is probably the sport Portugal is best at. As of 2014, Spain has won the world cup 16 times and Portugal 15 times, but Portugal has a total of 38 medals against Spain’s 35. Just a pity that Portugal seems to need to host the world cup to win it: only 5 of those 15 gold medals were won abroad.
The stamps were designed by Jaime Martins Barata, lithographed by the Mint on wove paper sheets of 10×10 stamps with perforation 14, and circulated from 28 June 1952 to 23 May 1955.