。
I'm thinking of pitting you against Yoshida in the race.
Literal
I [topic-は] race [at-で] you [object-を] Yoshida [to-に] oppose-[causative-させる] [nominalizer-こと] [object-を] am-thinking [explanatory-んだ].
対抗させる (たいこうさせる) — 対抗する ('to compete against') in causative form, meaning 'to make [you] compete against.' ~ことを考えている ('am thinking of doing'). んだ explains the speaker's plan. A structurally complex sentence with embedded causative.