Big Win Improvements
Every basho, it seems, has one rikishi who manages double-digit wins after having an awful basho two months earlier. In order to see if there was any way to predict it, I've gathered together every wrestler who went from losing 9 or more matches to winning 10 or more since the Nagoya 2011 basho. (Why Nagoya 2011? Look here.)
This information was gathered from the wonderful Sumo Database. That does make the parameters somewhat specific, but it notably avoids any wrestlers who went kyujo. This is not a list of rikishi who recovered from an injury and greatly improved. Everyone here was just bad for one basho, then turned it around. They might have been injured, but always mounted the dohyo.
The full list is at the bottom of this post. In total, 38 separate wrestlers have achieved this strange feat a total of 81 times over the 55 basho. First, we'll look at the big takeaways.
Not Every Basho has a Big Gainer
While it seems someone is always getting a lot more wins than the last time out, the phenomenon will occasionally skip a basho. In the Nagoya 2019 basho, only Terutsuyoshi achieved the feat, going from 6 wins to 12 wins between May and July. But no one did it from Naru to Hatsu.
Conversely, sometimes the big gains come in batches. In March, four wrestlers, Abi, Ichinojo, Kotoshogiku, and Ryuden all saw large improvement. There isn't just one, nor is there a guarantee of one.
It Takes a Different Rank to Get Some Different Records
On average, these wrestlers saw a drop of four-and-a-half ranks. By "rank," I mean that every slot on the Banzuke is one "rank." So Yokozuna, Ozeki, Sekiwake, and Komusubi are all individual ranks, as are each numbered Maegashira.
By that reckoning, most of the rikishi who performed this trick began about Maegashira 3 or 4, then ended up about Maegashira 8 or 9. So if you want to find someone who might rebound, that's the formula.
It should be noted that three Ozeki, Kotoshogiku, Goeido, and Terunofuji, achieved the feat at Ozeki over both basho. The banzuke has also been nice to Sekiwake and Komusubi who lose big, so some rikishi made the list after small tumbles. Generally speaking, though, if someone has a change in rank that makes them face different competition, they might just improve.
The Highly Volatile Rikishi
Some sekitori appear on this list more than others. It is probably not a good thing, as in order to make the list in the first place you have to lose a lot. Yet they also show the ability to hang on and win in the next basho.
Ikioi, Takayasu, and Tochiozan share the record for making the make-koshi/kachi-koshi and then some leap. Gagamaru mad the same turnaround 4 times, a feat replicated by Aoiyama and Endo. It's hard to spot a pattern with this grouping, other than they are all of decent size. Some rikishi are just more volatile it seems, whether they use a variety of approaches like Endo or are fairly predictable like Aoiyama.
The Biggest Turnarounds
And here is the fun bit. Between Kyushu 2011 and Hatsu 2012, Gagamaru went from 2 wins to 12 wins. Endo improved from 3 to 13 wins from Nagoya 2016 to Aki 2016. Yutakayama repeated Gagamaru's 10 win improvement by going from 2 to 12 wins between Natsu 2018 and Nagoya 2018.
That's the best improvement in this group, but six times a 9 win jump has happened and 8 win jumps have occurred five times. Big jumps like this happen, but it's not absolutely common. It also seems there isn't a good way to find who.