Which clubs have retired shirt numbers?

"Are Milan the first club to retire a number as a mark of respect for a player's retirement as they have done for Franco Baresi?" asks Karl Walsh.

"West Ham have certainly done it for Bobby Moore," replies Paul Bestall. "It's not that rare, to be honest, escpecially in American sports, with Michael Jordan's No23 and Scotty Pippen's 33 at the Chicago Bulls probably being two of the most famous retired shi ..."

Yes, yes, but there are others we should mention back in the world of Association Soccer Football. Firstly the case of Paolo Maldini, whose shirt is not fully retired, as the Milan legend has given permission for the club to reissue the No3 shirt should either of his sons play for the Rossoneri.

The most famous retirement is surely an unsuccessful one: the Argentinian Football Federation decided to retire Diego Maradona's iconic No10 shirt in 2001, and submitted their 23-man squad list for the 2002 World Cup numbered one to 24, with the 10 omitted. The list was flung back in their face, Fifa telling them to do it properly, and to get their feet off the table t'boot.

Seven clubs in England and Scotland have retired a number, but most as a result of a player's sudden death. Hartlepool (Michael Maidens, No25), Manchester City (Marc-Vivien Foe, No23), QPR (Ray Jones, No31), Wycombe (Mark Philo, No14) and Aberdeen (Hicham Zerouali, No20) have all withdrawn numbers in the wake of tragedy. Elsewhere, Chelsea's No25 shirt has been left unused in the wake of Gianfranco Zola's stellar Stamford Bridge career, while West Ham left 15 years between Moore's death in 1993 and the announcement of their No6 shirt's withdrawal.

Perhaps the nicest story is Ferencvaros's retirement of their No1 shirt in honour of Gyula Grosics. The legendary Hungarian goalkeeper wanted to sign for the club in the 1960s, but was refused permission to do so by the communist regime running the country at the time. In 2008, that wrong was at least partially righted when the club signed the 82-year-old, let him kick off then stand in goal for a few minutes in a friendly against Sheffield United, then retired his shirt. Now 83, the 1954 World Cup runner-up is still technically a player for the club.

Many more shirts around the world now lie unused, something you can read about thanks to our good friend Jimmy Wales.

OLD-SCHOOL PLAY-OFFS

"According to this excellent website there was an FA Cup third-and-fourth-place play-off staged in 1970-71 between Everton and Stoke," writes Tom Moore. "I never knew these games existed. Were they played every season and when were they introduced/scrapped?"

They were played every season from 1970, Tom, but only for five years after proving unpopular with players and fans. The FA even experimented with holding the game in August – shortly before the beginning of the following season – in 1972 and 1973, but this failed to win over the doubters, and the last such play-off was played between Burnley and Leicester City on 9 May 1974, with the Clarets winning 1-0.

The play-off did produce one significant first, however. Birmingham's victory on penalties after a 0-0 draw against Stoke on 5 August 1972 was the first time any FA Cup tie had been decided on spot-kicks.

PANA'S PENALTY PALAVER

"While trawling through the rsssf.com archive at work I found a curious result from a first-round tie between CSKA Sofia and Panathinaikos in the 1972-73 European Cup," said Ciaran McLoughlin. "It states that the second leg was replayed due to 'errors in the penalty shoot-out procedure'. Does anyone have any ideas what these errors were?"

"CSKA and Panathanaikos each won their respective home legs 2-1, so the second leg in Athens went to penalties," explains Sean DeLoughry. "CSKA scored their first three, while Pana missed two of their first four. At that point, with the score 3-2, the Russian referee Valentin Lipatov declared CSKA the winners – having failed to realise that Pana could still draw level if their opponents missed both their remaining penalties. Quite how it wasn't sorted out there and then is a mystery, but Panathanaikos appealed and the match was annulled. CSKA then won the replayed second leg anyway, winning 2-0 in Athens."

Do you know of any other penalty shoot-outs voided in similarly random circumstances? Let us know at knowledge@theguardian.com.

KNOWLEDGE ARCHIVE

"Has a physio ever been sent off?" wondered Dave Griffiths back in 2006.

In 1989, the mild-mannered Gary Lewin managed to attract the ire of the ref during a pre-season friendly between Arsenal and Independiente in Miami. When Gus Caesar went down injured, Lewin - thinking he'd been given permission by the ref Paul Dominguez - ran on to treat him. Unfortunately, Dominguez saw this as a threat to his authority and banished Lewin to the bench. As it turned out, Lewin needn't have bothered: Caesar was sent off shortly afterwards, but Arsenal still managed to win 2-1 and lift the coveted Zenith Challenge Trophy.

Can you help?

"I read somewhere recently that Celtic were awarded only one penalty in 30 years (1905-1935)," writes James Lavelle. "Can anyone verify that this was the case? And if it's true, is this a record?"

"After reading that Volkswagen reportedly shelled out €1m on Wolfsburg's title party, I got to thinking: what is the most expensive championship celebration in history?" asks Paul Myler.

"While in Adelaide to attend the wedding of his daughter recently, former Middlesbrough manager Bryan Robson attended a training session of the Port Adelaide Power Australian Football League team," begins Graham Clayton. "Robson gave the coaching staff of the Power some tactical tips. Have there been many other examples where football managers have advised coaches/managers of other football codes and sports?"

Send your questions and answers to knowledge@theguardian.com