The phrase "spike in thefts" is a noun phrase. It indicates a sudden increase in thefts. If you have a graph of thefts, you would see a sudden rise in the line, which would look something like an actual spike (which is a pointy object resembling an extremely large nail).
part of speech
Adjective
What part of speech is thaw
The part of speech for oscillate is verb.
An adjective is a part of speech.
You spike a volleyball with the palm of your hand.
The word is spelled thefts, just as you spelled it. Thieves would be the plural noun, or the persons committing the thefts.
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
spike lee
The part of speech for "unfamiliar" is an adjective.
The part of speech of "came" is a verb.
The part of speech for "twirl" is a verb.
The part of speech for "explicit" is an adjective.