IT'S been a tough start to life at Parkhead for Boli Bolingoli. Stepping into Kieran Tierney's shoes was always going to be a big ask whoever his replacement was, but the Belgian has so far struggled to adapt to life at his new club.

On Bolingoli's home debut, the left-back was at fault for Sarajevo's only goal. When Celtic travelled to Romania for their Champions League qualifier against Cluj, the defender had a torrid time as Celtic laboured to a 1-1 draw. And then for the return leg, Neil Lennon dropped him altogether to fit Olivier Ntcham into the team, preferring to start Callum McGregor in defence.

It's fair to say that the 24-year-old hasn't exactly hit the ground running at Celtic Park but it is still early days for Bolingoli and there is a feeling that we're yet to see the best of the former Rapid Vienna player. But there is no denying that Bolingoli has looked suspect defensively, which begs the question: is he really a left-back?

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The diagrams above detail some interesting heat maps that suggest Bolingoli is perhaps better suited to a role on the left of Celtic's midfield. The first shows the Belgian's average position in his first seven games in Lennon's side and it is interesting to note that he spends the majority of his time in the opposition half. Modern full-backs are, of course, given more attacking repsonsibility than ever before but even so, this heat map is particularly unusual.

The second and third heat maps highlight Bolingoli's average position at Rapid Vienna last season and the areas of the pitch that Kieran Tierney occupied last season as a way of comparison and while both still spent much of their time in the opposing team's half, in both instances they spent their fair share helping out defensively too. This season, though, Bolingoli simply hasn't been pulling his weight defensively.

This may be the result of Lennon's tactics. The Northern Irishman plays a direct brand of football that requires his full-backs to bomb forward and contribute to attacking play. But when we dig into Bolingoli's defensive numbers, the results make for grim reading for Celtic supporters.

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The most worrying figure regarding Bolingoli is that the Belgian really struggles when it comes to winning the ball back. So far at Celtic, Bolingoli fails more tackles than he wins, with a success rate of just 42.5%. Tierney, for example, was winning 71% of his defensive duels last season. The new Celtic signing is also giving away more than three times as many fouls than Tierney did, which is something that could surely harm Celtic in future.

Comparing Bolingoli's defensive stats to Tierney might be a little unfair, but it is worth emphasising how low a success rate this is. There isn't a defender in the Scottish Premiership posting such low numbers in this regard. And this is fairly typical of Bolingoli; in the previous three seasons at Rapid Vienna, the defender's tackling success rate was below 60%.

The game against Cluj in Romania highlighted just how suspect Bolingoli can be in defence. He won just three of his 12 defensive duels, gave the ball away on both occasions he attempted to dribble forward, lost the ball three times in his own half and only 14 of his 35 passes found their intended target. In short, he was rubbish.

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It doesn't look as though Bolingoli is the answer to Celtic's defensive dilemma, but that is not to say that he has no future at Parkhead. Going forward, Bolingoli has actually looked quite effective. 80% of his overall passes for Celtic have been successful, Bolingoli's (37.5%) crosses are more accurate than Tierney's were last season (35%) and his forward passes (77.3%) are also an improvement on Tierney (72.6%).

Bolingoli's Celtic career has got off to a poor start but the 24-year-old can certainly contribute effectively in Glasgow's east end. If handed a role on the left of midfield, the data suggests that Bolingoli could thrive. But so long as he's played in defence, playing a role that he is simply not suited to, the numbers make it clear that he'll struggle. Bolingoli does not possess the defensive nous to justify his inclusion in the Celtic defence, but he could thrive further up the pitch.