*Here “when” is supplied as a component of the participle (“saw”) which is understood as temporal
*Here “by” is supplied as a component of the participle (“reviling”) which is understood as means
*Here the direct object is supplied from context in the English translation

In other versions

ESVEnglish Standard Version

But when the Jews saw the crowds, they were filled with jealousy and began to contradict what was spoken by Paul, reviling him.

NIVNew International Version (2011)

When the Jews saw the crowds, they were filled with jealousy. They began to contradict what Paul was saying and heaped abuse on him.

CSBChristian Standard Bible

But when the Jews saw the crowds, they were filled with jealousy and began to contradict what Paul was saying, insulting him.

NLTNew Living Translation

But when some of the Jews saw the crowds, they were jealous; so they slandered Paul and argued against whatever he said.

KJV 1900King James Version

But when the Jews saw the multitudes, they were filled with envy, and spake against those things which were spoken by Paul, contradicting and blaspheming.

Public Domain