Study to Compare the Efficacy and Safety of NT 201 (Botulinum Toxin) With Placebo for the Treatment of Lower Limb Spasticity Caused by Stroke or Traumatic Brain Injury

The purpose of this study is to determine whether a single treatment with administration of 400 Units NT 201 (botulinum toxin) is superior to placebo (no medicine) for the treatment of lower limb spasticity caused by stroke or traumatic brain injury (Main Period). Participants will be assigned to the treatment groups by chance and neither the participants nor the research staff who interact with them will know the allocation. The following 4 to 5 treatment cycles will investigate the safety and tolerability of treatment with NT 201 (botulinum toxin) when administered in doses between 400 and 800 Units (Open Label Extension Period). All participants will receive the treatment and the dose will depend on whether only lower limb spasticity or combined upper and lower limb spasticity are treated.