Get Score value
import com.atlassian.jira.component.ComponentAccessor
def issueManager = ComponentAccessor.issueManager
def customField = ComponentAccessor.getCustomFieldManager().getCustomFieldObjectsByName("Score")[0] // Your Score custom field by name
def issue = issueManager.getIssueByCurrentKey("TESZT-51")
def value = issue.getCustomFieldValue(customField) // Your Score value, returns Double
log.warn("Your Score value: " + value)