When Ireland played Scotland in the Lansdowne Road qualifier last year, there were strange men with Irish accents wandering around the pubs afterwards, getting in the faces of Scottish supporters.
"Glasgow's green and white!" they would holler. They'd fix the random Scot with a stare. They were trying to gauge the response. This would tell them what they needed to know.
One Scottish supporter with whom Balls had been conversing, a man called Fraser, appeared simultaneously put out and confused. His indifference might have indicated he was a Rangers man. He confirmed quickly that he was an Aberdeen man and hated both sides of the Old Firm.
The question of Irish people supporting Celtic when they play League of Ireland clubs has long rankled with supporters of domestic football.
Irish teams have met Scottish sides plenty over the years. And in the 21st century, we seem, dare we say, to be gaining the upper hand, at least when it comes to the non-Glasgow sides. Here's the rundown of Irish-Scottish encounters in the European Cup/Champions League and the UEFA Cup/Europa League.
Waterford United v Celtic, 1970
Shamrock Rovers were the first Irish club to play in the European Cup in the third year of the competition's existence in 1957.
It wasn't until 1970-71 that an Irish club won a match in the European Cup. And that wasn't against another club from the island.
Waterford United smashed Glentoran 4-1 on aggregate, winning 3-1 in the first leg in the Oval.
The reward was a tie against Celtic, two and a half seasons after they won the European Cup.
Celtic were proper European kingpins and Waterford were badly out of their depth. They lost 7-0 at home in the 1st. leg. Lou Macari, Bobby Murdoch and the patriotically named William Wallace did the damage.
With the tie over, they put in a stirring show in Park Head, going 2-0 ahead before half-time, before succumbing 3-2 after the break.
Bohemians v Rangers, 1975
Bohemians came strong in the latter part of the 1970s, winning two League titles in 1975 and 1978. In their first foray into the European Cup, they were soundly beaten in Ibrox.
In the return leg, they fought Jock Wallace's team to a 1-1 draw with Turlough O'Connor grabbing a second half equaliser.
1975: Derek Johnstone scores as Rangers take a 1-1 draw in Dublin against Bohemians in the European Cup 1st Round 2nd Leg.
— On This Rangers Day (@Rangers_today) October 1, 2016
Dundalk v Celtic, 1979
The farthest an Irish club has gone in the European Cup. Dundalk beat Linfied (we could always count on beating the Northern clubs, save for 1984) following a 1-1 draw in Oriel Park and a 2-0 win in the 'away leg' in Haarlem. The first leg was mainly memorable for the violence.
A 2-1 win the next leg over the Maltese champions Hibernians FC (another Irish team) and they earned the right to face Celtic in the final 16. They were far from out of place too.
They only lost 3-2 in Glasgow with goals from Cathal Muckain and Mick Lawlor. Qualification to the quarter-finals looked a serious possibility.
The match finished 0-0 in Oriel Park. A bandaged Dermot Keely said the full-time training was the difference.
Bohemians v Rangers, 1984
The Rangers fans came to Pisser Dignam's Field in 1984 and made shit of the away end. Bohemians fans flaunted their fondness for the Vatican flag in response.
The match has usually been overshadowed by the provocative displays and the flag burning on the terraces. But it was a proud night for the League.
Bohemians won 3-2 with Gino Lawless smashing home the winner five minutes into the second half.
The Today Tonight report on the aftermath is preserved on the youtube channel of the great killianm2. Rangers won the second leg 2-0.
Bohemians v Dundee United, 1985
The 1980s was a busy time in Scottish-Irish football relations. Five years running, teams from both Leagues collided in European competition.
Bohs met Jim McLean's Dundee United in the 1985-96 UEFA Cup. Their opponents had been Scottish champions a few years before and shone in Europe's secondary competition.
It was in this era that they famously beat Terry Venables' Barcelona, as Eamon Dunphy had cause to remind the Irish people some years ago.
Dundee United coped much better in Dalyer than Rangers. They won 5-2 with a hattrick from Paul Sturrock. Bohs managed a 2-2 draw in Tannadice with goals from Jackie Jameson and Rocky O'Brien.
Shamrock Rovers v Celtic, 1986
Pat Fenlon described the Shamrock Rovers team that won four League titles in a row as the best team he'd ever seen play in the League of Ireland.
That Rovers side boasted Irish internationals Pat Byrne, Liam O'Brien and Peter Eccles in the squad, along with Mick Neville, Dermot Keely, John Coady and Mick Byrne.
However, they failed to make any real headway in the European Cup, even losing on away goals to Linfield in 1984 - the only time an LOI side lost to an IFA team in European competition.
But they performed respectably against Celtic in 1986, losing 3-0 on aggregate.
18,000 spectators packed into Milltown for the first leg, with roughly one third of the crowd being Scots. There was much chatter about switching the game to Lansdowne Road but they decided to stick with Milltown.
It was only seven minutes from time when Celtic got the game's only goal - a breakaway strike from Murdo McLeod. In the Glasgow for the return, Mo Johnston scored twice to secure Celtic's place in the next round.
The tie was distinguished by unusual levels of camaraderie between both sets of fans.
Bohemians v Aberdeen, 1987
Alex Ferguson was gone and the Old Firm was in the process of re-establishing its absolute stranglehold over the Scottish League. But Aberdeen were still a relevant force.
Jim Ball's strike in the second leg in Pittodrie was the only goal of the tie. But the Scots weren't so lucky 12 years later.
St. Patrick's Athletic v Hearts, 1988
St. Patrick's of Dublin, as the Scottish sports reporters called them, were demolished 4-0 on aggregate by Hearts. They'd go onto reach the quarter-finals where the fell to Bayern Munich.
St. Patrick's Athletic v Celtic, 1998
The 1990s were a democratic era in Irish football with a number of different clubs stealing a League title. But St. Pat's were the team of the decade, winning three championships in four years between 1996 and 1999.
Pat Dolan's St. Pat's team achieved a spirited 0-0 draw in Celtic Park in August 1998. They soaked up the acclaim of their supporters.
Celtic won 2-0 in the second leg. Anecdotal reports tell us that Celtic's Scottish supporters were the epitome of class. Their Irish based supporters were less so.
"Fuck off back to England", one Dubliner roared at St. Pat's Scottish striker Ian Gilzean.
Shelbourne v Rangers, 1998
Fears that Rangers supporters would wreck the gaff as soon as they touched down on Irish soil had led Shelbourne to relinquish home advantage. Bizarrely, they had to play their home leg in Prenton Park.
The match is only remembered now for the surreal opening when Shels went 2-0 ahead. Early in the second half, Pat Morley dinked the keeper and made it 3-0. Very rarely is the rest of the game even shown.
Quite right too. Rangers re-gathered themselves and won 5-3. They won 2-0 in Ibrox.
Many of the Shels fans missed the early burst. The police had held them back for their own safety as they sorted what Karl McGinnity described as "a cantankerous horde" of Rangers fans.
Mark Rutherford blasted home in one of his final games for Shelbourne. New manager, the grizzled veteran Dermot Keely told that he'd no place for him.
Bohemians v Aberdeen, 2000
Victory at last. Bohemians became the first Irish club to beat a Scottish side in European competition.
Roddy's boys won 2-1 in Pittodrie, with Trevor Molloy blasting home the winner from a penalty with three minutes remaining.
The home tie, which was played in Tolka Park rather than Dalymount, was scoreless until the final minute when David Morrison's own goal set the scene for an unbearably tense injury time.
But they held out to win on away goals. In the next round, they would beat Kaiserslautern 1-0 away from home.
Derry City v Gretna, 2006
The first team that Stephen Kenny brought to Europe was Longford Town in 2001-02. With Derry City, he built a phenomenal side who'd been languishing before his arrival. They fell just short of a League title in the mid-noughties.
He took them to the brink of the Europa League stages in 2006-07, losing narrowly to Paris Saint Germain in the final qualifying round.
Before that they beat IFK Goteburg and smashed Gretna 5-1 in the away leg in the second qualifying round. The game in the Brandywell a mere formality.
He has to be next Ireland manager, according to Pat Dolan.