The phrase "like an amateur" implies a lack of skill or experience in a particular activity. There are several synonyms to describe someone who is performing like an amateur. These include inexperienced, unprofessional, unskilled, inexert, unpracticed, and unqualified. When someone is described as an amateur, it implies that they lack the level of expertise or knowledge that is expected in a particular field. The use of synonymous terms can be helpful in avoiding negative connotations associated with the word "amateur". Overall, using a range of descriptors helps to convey an appropriate level of expertise when discussing someone's skills or performance.