On April 19, 2017, during the second period of the extra time of the second leg of the Champions League quarter-final match between Real Madrid and Bayern Munchen, Cristiano Ronaldo scored his hundredth UEFA Champions League goal (which was also his third goal of the night).

Was Ronaldo offside at the moment the final pass to him was made? Here is a picture of him receiving the ball from Marcelo before scoring:

enter image description here

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    The offside line used in that image is horribly misleading as to whether the decision is correct. The official also seems to be trailing approximately level to the defender in red, so how it wasn't flagged, I don't know...
    – Nij
    Apr 19, 2017 at 7:24
  • @JeopardyTempest there are parallel lines in the grass (the different shades of green) so you can recreate the vanishing point for the lines parallel to the goal line which in turn lets you draw other parallel lines. But the shaded area is off parallel in the wrong way. Apr 19, 2017 at 11:44
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    @ratchet freak, that there are, though unless the camera lens is circular (unlikely), I don't believe they should converge reliably. And minor errors in line diagnosis may lead to significant shifts in vanishing point? Apr 19, 2017 at 11:59
  • @ratchet freak: I'm certainly no industry expert on such topics, just subjects I've had to work with at times in the past. I may sound like I'm trying to debate it, but really have no position on the game (and didn't see it). Just giving my view when shown the image, and reasoning. Since the SE request is that comments not be answers, and I felt I had a bit too much of one, I moved my comments into an answer, and am deleting my comments, so feel free to provide any pertinent details there :-) Apr 19, 2017 at 12:03
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    The "watermark" on this image show this written: "Real Madrid ruling clubs since 1902". So I believe this is not a good source to show in an objective question
    – Ale
    Apr 19, 2017 at 13:29

2 Answers 2


Laws of The Game; Law 11 - Offside; 1. Offside Position state that:

A player is in an offside position if:


any part of the head, body or feet is nearer to the opponents’ goal line than both the ball and the second-last opponent.

It's obvious that Ronaldo was nearer to the goal line than the the second-last opponent (the guy in the red shirt: Mats Hummels).

Now the dubious part is whether Ronaldo was nearer to the goal line than the ball. The answer is yes, he was, hence, he was in the offside position.

Why? Because the offside-line in the picture you use is not quite parallel to the goal line, but look at another picture from goal.com, Ronaldo's head was closer to the goal line than the ball:

Ronaldo offside

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    @gdrt Many Madrid supporters say that Ramos own goal was offside as Lewi was in offside position and he interrupted in play though he did not touch the ball. Questions is,was that offside or legal?
    – Ganesh
    Apr 20, 2017 at 4:36
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    @Ganesh, It was illegal, because this goal was also scored when Lewandowski was in active offside position, as confirmed by Sky Germany. Look at 1:28 in the video, as you can see Lewandowski was closer to the goal line than the ball.
    – gdrt
    Apr 20, 2017 at 9:24

Looks like gdrt gave the rule well (and answered something I've wondered about for a long time too!)

But some of the complexities to the details make it appear close enough that I'm not sure all impartial arbitrators would agree that is a clear-cut offside call, in particular using this picture.

It may not be noticeable to the eye, but the lines drawn aren't parallel. I verified this in GIMP by copying the line for the penalty box and translating it left:

offside If you look closely, you'll note the increasing green between the previously drawn line and the shifted penalty box line I overlaid as you go up the image. Of course the resolution of that image isn't great, making it all that much more challenging to perfectly diagnose the line.

Then again, the big problem is that lines SHOULDN'T be exactly parallel, as there is always some perspective (angle change of truly parallel lines). See how much the lines change angle in this image:

(Source: Okiespavement.com)

Perspective depends upon the distance, height, and lens shape on the camera. That picture of the American football field seems setup to exaggerate it. But the result is that, unless the camera is situated on the line of interest (or a continuation of that line), or is directly above/below that line, any camera view can be surprisingly dubious (I've seen so many times where two views from similar locations appear to show different things due to very slight changes in perspective). The fact that the top and side of the penalty box do not make near a 90 degree angle makes me more suspect there is quite a bit of perspective in this picture, though the camera location would need to be known to have more clarity on this. Also note, the perspective can actually converge in either direction due to the shape of the camera lens (and angle of the camera?), so the American football field image doesn't necessarily help determine the proper perspective changes either.

Now, there is the possibility that perhaps the line shown in the image was actually provided by the broadcasters themselves, and that they calculate it based upon the actual geometry of the camera similar to the NFL's 1st and 10 line. That would make it a lot more reliable. I've still seen such systems be imperfect, but it would allow a little more assurance that it is fairly correct, if we knew that they did that. With the trend towards replay officials in soccer, it would seem very important to be able to overlay a properly calculated line reliably onto cameras, taking into account all camera details. Here's to hoping they do that and make clear they are doing that.

That challenge of camera perspective, plus the added difficulty in determining the exact moment the ball left his foot, leads me to suggest it may be too close to say for sure.

In American football we face so many situations in our replay system where things are unclear or debatable that we require so-called "indisputable visual evidence" to make a call. Now what exactly that is... becomes a question in itself! But from my impartial perspective regarding the game (which I didn't see) (and for what it's worth, with that slight background in geometry and a bit of collegiate intramural refereeing experience) I would only suggest that Bayern fans would perhaps be best off not feeling particularly hard done by such a call, as it is quite close... and there continue to be many worse calls made and allowed to stand.

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    Your picture is worse than the one given in the OP! The offside line and the edge of area line should converge away from the camera, not diverge.
    – AndyT
    Apr 19, 2017 at 14:03
  • @AndyT I know it looks like my lines diverge, but if you read my details, you'd see it's just the actual line translated graphically, so that is deceptive. I made no attempt at convergence/divergence, just a direct copy, showing the questionable nature of the other picture. But as I stated, lens shape is everything, and without knowing it, you cannot say where they should converge... Apr 19, 2017 at 21:07
  • Ok. So you're saying "The lines shouldn't be parallel. I've proved that the line drawn in the OP isn't parallel to the edge of the area. Therefore the line in the OP has made some attempt at perspective, but I make no comment as to whether it's a good attempt or not." ? I guess that's not too bad an answer. To my eyes the line drawn in the OP is incorrect (and favouring Ronaldo). How far it is incorrect is unclear, but given that the line drawn is right on the limit for both his head and knee, he is almost certainly offside, but it's close enough that you couldn't expect the linesman to know.
    – AndyT
    Apr 20, 2017 at 8:24

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