At 9 months Will's standing balance with hand support has improved, but he still manages to topple over quite frequently.
Postural sway
Notice the large amount of sway seen in the pelvis as he explores the options for maintaining his CoM over the BoS. This postural sway represents the development of internal models for controlling the integration of sensory information from the body as well as the task demands of his goal directed actions.
Pull to stand - transition from floor sitting to standing
At 9 months Will is able to transition from floor sitting to standing with support through half kneeling. He does this smoothly, using momentum as he transfers weight onto the forward leg. This is a tricky movement because he has to control hip and knee extension, as he shift the weigh onto the forward leg which involves a large lateral shift of the pelvis over the supporting lower limb.
Stand and lean
Although Will can stand with support on one hand, he often needs both hands for engaging with a toy. When this happens he leans forwards and rests his chest against the foam blocks, which provides more stability and allows him to use both his hands for manipulating the toy.
Looking behind - twisting
Infants will often turn to look behind them. At 9 months Will manages to twist and stay upright.
But on other occasions, depending on the position of the legs, he does not make the necessary adjustments in weight distribution over the feet and the twisting action results in a fall.
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Will 9 months standing with hand support