The phrase "pinning it on" generally means to assign blame or responsibility for something. Antonyms for this phrase would include "absolving," "clearing," "exonerating," "exculpating," and "vindicating." These words convey the opposite meaning, suggesting that someone is being released from responsibility for a particular action or situation. For example, "after investigating the situation thoroughly, the authorities completely exonerated the suspect." Other antonyms that could be used include "acquitting," "justifying," and "pardoning." These words all indicate that someone has been found not guilty, or that their actions have been deemed acceptable or understandable.