Spot takes an object followed by -ing when you notice a person or thing engaged in an activity. Bare spot + object + infinitive is not the ordinary parallel construction documented by the learner dictionary.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Use “spot someone doing something” when you notice the person in the act. Avoid bare “spot someone do” for the same meaning.
Key details
Confusion Familygrammar-and-usage distinction
Rule Familyverb-complement and object pattern
TermsSpot Someone Doing, Spot Someone Do
Further guidance
Boundary
Spot has other direct-object and clause patterns; those do not license a bare infinitive as an interchangeable event complement.
Construction
Oxford documents spot + object + -ing for noticing an activity.
Decision
Use doing for the observed activity; otherwise recast with a clause if you need a different event perspective.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
Oxford directly documents “argue somebody into doing something” for persuading somebody by giving reasons. The cited construction evidence directly supports into + -ing; it does not license “argue someone to do” as an equivalent complement pattern.
When ask means request an action from a person, Cambridge documents ask + person + to-infinitive. Bare “ask doing” is not the ordinary request complement for that meaning.
Cambridge directly documents both badger + object + into + -ing and badger + object + to-infinitive for repeated pressure or requests that push someone toward an action. The verb also covers repeated questioning, so context must show whether the sentence is about persistent persuasion or interrogation rather than assuming every use names a requested action.
Cambridge directly illustrates bamboozle + object + into + -ing for deceiving someone so that the person takes an action. The cited entry does not establish bamboozle + object + to-infinitive as an equally documented alternative, so this guide does not manufacture a two-way rule.
Cambridge explicitly documents beg + object + to-infinitive for an urgent request and also records beg for + noun and other request patterns. A following -ing form may appear elsewhere in a sentence, but it is not the ordinary replacement for the documented object + to-infinitive request construction.
Cambridge gives direct evidence for beguile someone into doing something in the literary persuade/attract/deceive sense. The cited entry supports the into + -ing construction; it does not establish beguile + object + to-infinitive as an equivalent pattern for this meaning.
