An Irish FA appeals committee has ruled that the IFA's disciplinary body was wrong to reject a NIFL recommendation to take a case against Linfield over sectarian singing.
The case involves the Irish Premiership game between Larne and Linfield at Inver Park on 15 September.
The NIFL match observer heard "20 to 30" Linfield fans singing the 'Billy Boys' song for a two- minute period.
NIFL then asked IFA disciplinary chiefs to look at the observer's report.
NIFL chief executive Gerard Lawlor made it clear in a letter sent to the Irish FA disciplinary body on 18 September that NIFL's concerns related to the singing of the Billy Boys by the small group of Linfield supporters.
In its response on 29 September, the IFA disciplinary committee said that there was "insufficient evidence to warrant a notice of complaint under the breach of Article 32.2 to Linfield on this occasion, as the offensive words in the lyrics of the 'Billy Boys' song were not detailed in the match observer's report".
"With this in mind, the disciplinary committee would be grateful if you could gently remind all match observers of the level of detailed evidence required within their reports to allow the disciplinary committee to substantiate notice of complaints," added the IFA disciplinary committee in its response to NIFL.
IFA Disciplinary body must reconsider issue
After receiving the IFA disciplinary body's decision, Lawlor immediately wrote back to the committee expressing his "astonishment" at the verdict and later submitted a formal appeal which was upheld during a hearing on Thursday.
In its appeal ruling which BBC Sport NI has seen in full, the Irish FA appeals committee states that one member of the football governing body's disciplinary panel had told it that "he was unaware of the nature of the 'Billy Boys' song, although he did have an awareness that the melody was used innocuously in his old school song and in a local rugby club's song".
"The committee accepts that during their lives the respondent's members may have been sheltered from witnessing the singing of the 'Billy Boys' song, or that they have been otherwise disinterested in exploring its meaning and words, so that they either did not know the song or did not appreciate that it was an offensive sectarian anthem," continued the IFA's appeals committee.
"[But] The lack of knowledge on the part of the respondent's members or their uncertainty about what was being alleged and whether an offence could be proved, required the respondent to ask questions rather than simply reject the complaint without further enquiry."
The appeals body's ruling means NIFL's original recommendation on the matter will have to be reconsidered by the Irish FA's disciplinary committee and a decision reached by 12 November.
The IFA appeals committee ruling says NIFL chief Lawlor after being informed of the IFA disciplinary body's decision not to pursue a case against Linfield, submitted the "traditional lyrics" of the Billy Boys in full, saying that NIFL could not allow the singing of the song "to go unpunished".
In its official letter of appeal to the Irish FA on 3 October, NIFL stated that "there is only one traditional version of the song, and we feel the observer via the league provided all the evidence to the committee to warrant a notice of complaint".
"The song is offensive and widely accepted as such. We also enclose a copy of former rulings by both Uefa and the Irish FA in relation to the song and its inappropriate nature," added NIFL in its appeal letter.
The IFA appeal committee verdict does state the Irish FA disciplinary committee now concedes that it should have taken into account previous Uefa and Irish FA rulings in relation to the singing of the Billy Boys and that if it had done this, that Linfield would have been charged with breaching spectator conduct and discrimination rules.
However, Thursday's appeal verdict says "this concession is insufficient and incomplete since it rests on the basis that the respondent considers that the formulation of the complaint when it was originally referred by the appellant was inadequate".
"If the respondent was unsure about what was meant by 'a short rendition of the Billy Boys' with the traditional words of the song, we find that the respondent was obliged to seek clarification of the complaint before rejecting it.
"This committee is entirely confident in its view that very many people in Northern Ireland and elsewhere would have been left in no doubt that when the match observer referred to the singing of the 'Billy Boys' (using the traditional words), he was describing the singing of a song which was sectarian and offensive in nature."
'IFA should urgently review training needs'
The appeal decision goes on to express disappointment that "members of the IFA Disciplinary Committee have professed a lack of awareness, and as it seems to us, a low index of suspicion, when considering a complaint which featured reference to the singing of the notorious Billy Boys".
"Accordingly, the committee recommends that the Irish Football Association should urgently review the training needs of those who participate in its structures, particularly those who may be tasked with grappling with and adjudicating upon the sensitive issue of sectarianism in football, as well as those who are employed to support those structures.
"We have determined that the necessary next step, applying Article 14(6)(e) of the Appeals Committee rules, is to refer this matter back to the respondent for it to make a fresh decision whether to issue a Notice of Complaint to Linfield FC for breach of Article 32.2, 27.1 and 27.5.
"This matter should be considered by the respondent and a fresh decision reached within 10 working days," concluded Thursday's verdict.