There are several synonyms for the word "immobilising". One can use terms like "stopping", "restricting", "hindering", "paralysing" or "inhibiting" to replace it. All of these synonyms imply a sense of halting or obstructing something from functioning or moving normally. For example, "stopping" can be used in the context of "stopping the thief from running away", while "restricting" can be used to describe a situation like "restricting the movements of a patient due to a leg injury." In short, there are multiple synonymous words for "immobilising" that can be used to convey the same meaning with a slightly different tone.