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enter image description here
(Source)

Is that a Ram Air Turbine (RAT) on the port side below the wing? Why is it already deployed and spinning during takeoff?

This answer mentions a minimum airspeed at which RAT can be deployed.

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Raj
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The plane in your question is the Saab 37.

According to x-plane.org about this plane—

Emergency power is supplied by a ram air turbine just before the left wing leading edge, which extends automatically on hydraulic power failure, and just before touch down. (Earlier, it was also always deployed whenever the landing gear was down.)

They cite Air Power Journal, Summer 1993, various issues of FlygvapenNytt and other Swedish air force informational material.

The Swedish Wikipedia also says the same thing—

On some military aircraft, such as the Saab 37 Viggen, the RAT is used during takeoff and landing for the pilot to be able to maneuver the plane in case of an engine failure at low altitude.

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    Great find! Thanks. :) Any guess why this design is not the norm for all military aircraft....or even all aircraft? – Raj Jan 31 '17 at 15:51
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    @Raj, in most aircraft the hydraulic accumulators are large enough to cover the time until RAT deploys. – Jan Hudec Jan 31 '17 at 18:38