CARLTON will have to overcome history if it is to compile a September to remember.

Having lost three of its last four games, the club's defensive deficiencies have been exposed in disappointing losses to Greater Western Sydney, the Western Bulldogs and Port Adelaide that have the side's top-four hopes hanging by a thread.

A leaky backline has seen the Blues concede 86.6 points per game this season, ranked inside the bottom five across the entire competition for scores against during the campaign.

In fact, only Essendon (87.5 points) and cellar dwellers West Coast (99.4 points), Richmond (102.6 points) and North Melbourne (108.6 points) have conceded more than Carlton this year.

According to Champion Data, only five teams since 2000 have qualified for finals while being ranked inside the bottom five for scores conceded. They have never finished higher than seventh on the ladder, combining for just two finals wins.

No side since the Western Bulldogs in 2006 has won in September with such a poor defensive record, while no team since Essendon in 2009 has been to the finals with that type of fragility down back.

Leaky finals teams

While the responsibility for a leaky defence might typically be pointed at the backline, Carlton's issues seem to stem from the midfield and the side's ongoing inability to defend from stoppage.

The Blues have a strong midfield group, led by Patrick Cripps and Sam Walsh, which is reflected in the fact their +1.1 clearance differential is the sixth best in the entire competition.

But when they lose a clearance, they get hurt. Badly. According to Champion Data stats, the 42.1 points per game Carlton is conceding from opposition clearances is the second worst of any side in the AFL behind West Coast (42.2 points).

Meanwhile, the 13.5 points per game Carlton is giving up from an opposition's centre clearances is again the second worst of any side in the League behind only North Melbourne (15.9 points).

The Blues have appeared to be rotating fewer bodies through the midfield group to rectify such issues in recent weeks. Cripps, George Hewett, Walsh and Jack Carroll are the only players to have started 10-plus centre bounces in the last fortnight.

Meanwhile, Alex Cincotta has had more centre-bounce involvements than regulars including Adam Cerra, Elijah Hollands, Matt Kennedy and Lachie Fogarty across the last two matches.

But while finding the right formula currently remains a mystery for the Blues, pinpointing that mix could be crucial to the side's hopes of rebounding from this disappointing stretch and emerging as a premiership contender once more.