左右: positions on both sides and influence on a result
Compare one vase on each side of a stage with an expectation that weather will affect a game’s outcome, distinguishing the two senses of 左右.
The left and right sides of the stage
左右 (さゆう) can be a noun meaning left and right. Here, the stage is the reference for the two positions occupied by the vases.
“舞台の左右に、大きな花瓶が一つずつ置かれている。” says that a large vase is placed on each side of the stage. Keep 一つずつ: it is one on each side, rather than one vase across both sides in total.
The affected object in 左右する
左右する can mean influencing a result. Unlike the location phrase 左右に, this use identifies something that is affected.
“当日の天候が試合の結果を左右するだろう。” suggests that the weather that day will probably affect the outcome of the game. The weather is what may affect the game’s outcome, and だろう marks that effect as a conjecture.
Check the combination and the strength of the statement
左右に identifies the vases’ positions, while 結果を左右する concerns influence on an outcome. Do not insert the meaning left and right into the verb phrase.
The vase sentence describes an existing arrangement; the weather sentence expresses a conjecture about influence. It does not report a completed game’s outcome or establish weather as the only deciding factor.
Does the weather sentence report a settled game result and use 左右 to mean left and right?
Show the answer and why
No. 左右する means affecting the outcome, and だろう presents that influence as a conjecture. The positional sense appears in 左右に in the sentence about the vases.