Learn hiza-guruma in judo: off-balancing to the front corner, sole blocking at the knee, an arcing pull. With milestones, mistakes and clear knee-safety rules.
The honest answer: hiza-guruma, the knee wheel, is a foot throw. You break your partner's (uke's) balance to the front corner, block his front leg at the knee with the sole of your foot and turn him in an arc over this block. The German Judo Federation (DJB) does not name hiza-guruma in its compulsory list, but cites the pair sasae-tsurikomi-ashi/hiza-guruma as an example of a mix-up that should not count in gradings [1]. The throw is therefore a typical entry into foot techniques.
The rule frame is: judo is not a fight for points, but an ippon is only given if the fall is controlled until the ground [2]. That applies to you as tori too: the throw does not end with the block but with a controlled landing.
How long does it take? Expect several weeks until the block without a kick and the pull in an arc fit together (practical estimate, not a study). The knee is decisive: in a survey of 4659 judoka, cruciate ligament ruptures were the most severe type of injury, and for about one in three (32 %) the sport was lost for 6 to 9 months [3]. This guide therefore takes the knee seriously.
One hand on the lapel, the other on the sleeve. Upright, knees slightly bent, eyes ahead. Milestone: you can lead uke while walking without losing your own balance.
With both hands you pull uke toward his front corner until his weight lies on his toes and the outer edge of the front foot. That is kuzushi (balance break). A learning study with 64 children (on o-soto-gari, so TRANSFER) suggests that uchikomi with a preceding kuzushi helps with pulling and pushing, although group differences were not significant [4]. Milestone: uke stands on his toes and can hardly move the front leg.
You bring your standing leg close to uke, lift the other foot and lay the sole softly on the front of uke's knee (thigh attachment/knee, not the side of the joint). You do not kick, you block. Milestone: in uchikomi without a throw your foot stays calm on uke's leg, without pressure.
Both hands pull uke in an arc over the block, your upper body turns along. Uke rotates over his own block. Milestone: in slow motion uke turns without you yanking.
With your instructor's release you throw for the first time. You accompany uke with the pulling hand until the landing. Milestone: uke lands on his side in control, you stay upright.
The rule here: you are working with your partner's knee. An analysis of 17 videos of cruciate ligament ruptures in judo found that 65 % arose from direct contact, in 82 % of cases with the knee buckling inward (valgus) [5]. A survey of 43 cases added that the rupture mostly happened when being attacked and that mismatched grip styles (left-hander against right-hander) were more frequent [6]. Neither is a study of hiza-guruma in particular. But they show how quickly pressure against the knee becomes dangerous.
Therefore: the block comes softly and never as a thrust. Practise uchikomi (entry without a throw) for a long time before you throw. Uke must master ukemi and be able to tap or call "Mate!" at once. Club practice takes place under instructor control.
This guide explains and motivates; it does not replace supervised training.
Imagine your foot sole is a wall, not a hammer. The wall stands, and uke walks into it because you pull him. If you can hear the foot "slap" at the end of the throw, the block is too hard. A quiet foot is a good foot.
How to fit it into your week: practise uchikomi twice a week for five minutes, entry only, without a throw. Count ten repetitions per side with a calm partner. Only after three clean sessions do you ask your instructor for the first controlled throw. This is practical experience, not a study.
With hiza-guruma the foot sole blocks at the knee, with sasae-tsurikomi-ashi at the ankle, with a pull-lift action. The two are closely related, and the DJB explicitly names the mix-up as an example that should not count in gradings [1].
It can be if you kick or press sideways against the joint. In analyses of cruciate ligament ruptures in judo, direct contact at the knee was the most frequent mechanism [5]. With a soft block, uchikomi and supervision the risk is much smaller.
Expect several weeks for kuzushi, block and pull together. This is a practical estimate, not a study. A clean throw in free fighting (randori) takes considerably longer.
Only the footwork and grip change, for example in front of a mirror. You always practise the block at the knee with a partner, mat and instructor. Without a partner it remains shadow work.
Sasae-tsurikomi-ashi: How to Learn the Pulling-Lifting Foot Block Throw in Judo